Good question, I bet you're not the first to have it. Bixler has used the i86 in a build or two and seemed happy with it. About the only place to get a KK2 right now is on ebay for 75 bucks. The pirates are killing it.
While many people have success with the FC boards under $20, I agree with Tritium, you'll have a MUCH less frustrating experience if you get the KK2. I started with the Atmega168PA (v2.1) and then the Atmega328 PA (v3.0). The v2.1 never had a functioning yaw, the v3.0 worked sorta 'ok'.
The KK2 was an entirely different animal, and I loved it within seconds of taking to the air. And when updated to v1.5 firmware (all should ship with it by now), it'll make flying wonderful.