BOATLOAD

Buying the boatload is certainly the most cost effective way to purchase donuts. At $100 (US) for 2400 that makes them just over 4 cents apiece. The big problem I have is that when I have so many donuts I spend them more freely. Speeding up things, buying decorations that I don't really need just to increase my bonus percent, etc. So I would say go ahead and and do it if you have good self control or have plans for the majority of the donuts already.

Or give it to charity (Although, given the feelings for EA on this forum, buying donuts might be considered charity :) )