50 foils for $7 via Troll and Toad:
http://www.trollandtoad.com/p151656.html
100 foils for $12.50 from Star City:
http://sales.starcitygames.com/carddisp uct=426212
25 foil commons for $5 via ABUGames:
http://abugames.com/card139638-246665/M -Card.html
After checking through Ebay for about 30 minutes, I couldn't find any reliable sources of bulk foils, so I believe that these are your best options. Personally, I would go through trollandtoad, but that's because I simply refuse to give Starcity my money. Starcity may be the better deal, however.
I'm also willing to bet that any Game Store that deals in Magic (ie. Buys collections) will have a box of random foils that they would be willing to sell. One store that I used to go to had a fat pack full of spare Promo cards from various events as well that they just give away, so you could always ask for spare promos when looking for cheap foils as well.
Thank you very much!!! This is exactly what I was looking for. I tried my local shop, but they don't get enough transactions to get me the number of foils that I need.