Ok I am going to start with the Wench!
The wench is a fun character to play you can be a wife, a whore or single woman with this character. Anyone can be her! She was poor, which doesn't sound fun and there are laws of decorum, don't be rude to those above you, genuflect (that's bow and Curtsey), and watch your tongue around the Queen. Otherwise your day would have been spent working all day and playing when you could. While that sounds not much fun, at faires you have freedoms that those above you just don't. Your costume is also a lot more comfortable and if you lay in the dirt so what you can wash them when you are done. Velvet is a lot harder to clean then cotton :)
#1, #2 and #3 you need a good bodice!!! A bodice is different from a corset in that it is built much like a vest. A good bodice is designed for your body type. If you have a large Bust avoid a low neckline and get a well boned piece (steel bone only not poly boning). If you have a medium bust you can use a lower neckline to show off your clevage, and get a piece more focused on your waist line, for a smaller bust get something that is designed to give cleavage but isn't too low in the neck to diminish your assests. You want a bodice to be fitted, it is designed to nip in the upper torso and work as a bra. A good bodice does not need a bra.
This shop makes nice bodices, this is not Period (see the end of the article for why)
it is a great deal at $39.99 from http://wolfinsheepsclothing.etsy.com/ SOLD
This bodice would be good for A-D cup, it might be too low for a larger bust. The back laces add for a nice fit.
This bodice from http://peldyn.etsy.com/ is right on the edge of period, but since it has a pure navy reversible side, that would be period! Another good deal at $55
This bodice again would be good for approx an A-D cup.
This last cut is for those who work at less busty faires (for some reason certain areas are less busty), it is also an amazing cut for those with a larger bust who don't want the dreaded over flow look. With its tapestry material it would be period. This is pretty and will stand up to what ever you give it, for $80 from http://haverspanacea.etsy.com/
I also love the adjustable sleeves on this which helps to create a better fit.
If you are looking for a cheaper method an adjusted vest like shown in the Budget Pirate Wench post would be a great idea, you can also use a corset for a more piratey look.
Now for a shirt! There are many simple white shirts you can use but for a more period look a simple "chemise" is a great fit. The first is a half chemise, long nightgown length are period, but with the heat shorter examples like these are much more practical at most faires, from http://myfairelady.etsy.com/ for $27.50
The second is fun with a touch of color (yes your chemises can have color!) from http://ladymorgan001.etsy.com/ SOLD
I have to add while it looks cute, wearing your shirt off the shoulders is not period, so some of the more period chemises will not drop to that point.
Next we have skirts, traditionally a woman wore two skirts, one of the reasons is to add to the fullness of the hips (this was SEXY!), as well as to be functional as a apron of sorts. One is worn down the other is tucked up to the sides.
For simple skirts you can use peasant skirts or sew your own using a simple gored skirt design. I once used an A-Line skirt pattern, added two extra panels and went up a size, when the elastic or tied band is added it creates a simple and full look. I can't sew and skirts are the one thing I always make for my costumes.
A tiered skirt like this would also work though its not period from http://flamncodiva.etsy.com/ SOLD
You can add one of these shorter over skirts from http://loriann37.etsy.com/ for $14.99
This shop also offers a great deal on a long skirt for just $29.99 in your choice of color!
Peasants don't wear too much jewelry as it was of course too expensive, but a hat is a must! Hat's were worn by men and women of this period, lose hair was saved for special occasions such as May Day. Then women wore their hair long and flowing with flowers or head pieces like this one from http://friendlyfairies.etsy.com/ for $38
I normally don't like to add full costumes because I think its more fun to mix and match but I love this set from http://kritterville.etsy.com/ and at $89.95 it is an amazing deal so I just had to add it!
With the three pieces here you have a complete costume!
Lastly you can also wear what is called a Celtic Dress, it is for those who were Irish or occassionally by more middle class ladies
From http://kritterville.etsy.com/ for $89.95 for the full costume
And this one from http://peldyn.etsy.com/ for $170
PERIOD CORRECTNESS: If you are just looking for a fun costume skip this, if you are looking for something more period for working or fun, then read on!
King Henry IIIV introduced Sumptary laws to england which cover colors, materials and furs for all levels of soceity http://elizabethan.org/sumptuary/who-wears-what.html most commonly practiced across period faires is that only the Queen wears purple (since all of her family was dead) and Red in large amounts were saved for the Military.
While white was period, it was expensive to keep up since Clorox wasn't around to whiten the material easily or keep it white, it was usually saved for those with more "free time". In the period human or animal urine, with sunlight was used to bleach clothing, it was very time consumming. Most faires chose to allow white clothing even where it would not be period.
Heavy amounts of black in the clothing would have designated widows, clergy and puritans. All black should be saved for pirate costumes or the other characters mentioned above. Brighter colors were the norm, the dyes coming from nature. But watch for modern colors like neons, some pinks, and purple toned burgundys.
The last and most important is that while many materials are cheap and easy to find now, they are not period. Silks, Satins, Corduroy, Tafeta, velvet and Damask are period but above your station. Tapestrys are period, as are some other patterns if they are woven (if you see the pattern on the reverse of the material it is woven), they are correct for all classes. Watch out for shiny modern fabrics, they are not period! You can wear modern fabrics like blends if they look like natural fabrics. But many times you will find these materials do not breathe like natural fibers and one thing most faires are known for is being HOT so staying cool any way you can is very important!
Overall have fun, most people will not be judging your outfit based on period correctness unless you look so good they think you work at the faire! A good costume will last you for years and through a lot of fun times. Go and have fun being a Wench you!