Forget the "cheap" options. In the short run, they will be more expensive, even if they can do the job halfassed.

Better to save up a bit, and buy a good one to start with. We're using the IBF 4.5 in our raptors and feathers.
Not the most powerfull ESC, but those 2x40 Deutsche Grundlicheids ampères outshine the 320 Chinese ampère el cheapos in any respect.