When I was in my early 20s, I wore a tail all the time. I've more or less grown out of wearing a tail, unless I'm suiting. I also had a problem with my tails breaking a lot, because I'd wear them so often, I forgot they were there.
Anyway, good info on tails:
Go to ebay, look up 'fox tail', 'coyote tail', 'wolf tail'. Depending on coloration, fox and coyote are the cheapest.
Sometimes they will be real, sometimes faux. To me it honestly doesn't matter, but I'm sure others care. Anyway, ebay will normally have LOTS of tails (4 - 5 tails) for $30.
What I would do, is buy a lot for 30 bucks, and then make my own wearable tails out of them. I would keep the one(s) I liked, then I'd sell the other ones to friends $20 - $30. Significantly cheaper than what most people charge for tails, and raking me in huge profit.
All I did to "make" a tail, was gorilla glue a caribeaner(sp? those climber hook things) near the spine of the tail. Works way better than the annoying chains and sewn belt loops that are more common, in my opinion.
Anyway, that's my $0.02.
EDIT:
So I just went to ebay to doublecheck my facts, since this information is from about 5 years ago. Turns out not many people sell lots of tails anymore. But there are many listing for individual tails at around 5 bucks. So point stands-- make your own tail. It's cheaper.
For best results, search for the type of tail you want in this category:
http://www.ebay.com/sch/Hunting-/7301/i.html?_fcid=1&gbr=1&_clu=2