1. I'd go with some fabric fur, i.e fake fur, i'd never buy REAL fur.
2. I guess you could get it at a local fabric shop, thats where i got my fake fur.
3. Depends on how good quality you want and where you buy it, and how much you want of course. But for a pair of for ears, shouldn't be too much, for bout 200 SEK (~$28) i got enough fur to make myself 2 tails, 1 pair of ears and a pair of paws, and i still have some fur left.
EDIT:
Forgot to say that you'll need something to wear them (obviously), well, you can sew them on pretty much anything, i used a hat for my first ears.