Where do I find thousands of blue & yellow bricks for an art project? I'm an artist and I've started a project where I need around 4000 blue and yellow bricks, specifically bricks and plates that are 2x or 1x any length, but the longer the better. Any suggestions on where to find these for the best possible price?  

NOTE: I've purchased several used bulk lots on eBay, but on a price per brick I need basis, this isn't very cost effective. I've also gone to the LEGO store, but I you really can't get many larger bricks in those little cups, plus I actually prefer the look of used bricks. Any suggestions would be really appreciated. I don't have a lot of money as I'm a college professor, but I am having my first solo museum exhibition next fall and I'd really like to include this piece. (Sadly, unless you're world famous, museums don't pay a penny for artists materials.)
Try BrickLink.com, the Online LEGO Marketplace. It works like eBay, with buyers and sellers from all over the world. You can buy the exact pieces you need, in the quantity and condition you need.

Since you want a large bulk of parts, I would suggest that you post your request on the BrickLink Forum first, as there may be sellers who have a very large quantity of what you want, but haven't listed in their stores (sellers like to focus on listing their more expensive stock first). 

Most BrickLink sellers are good people and they would be happy to help out with a project like yours and offer very reasonable prices. It is also beneficial for them, as they can get rid of a large quantity of their stock at one time (especially if you are happy with used elements). So it's a win-win for everyone involved.