Cheap brushless esc options

I have just gotten back into the hobby and have no experience with brushless systems, so basically I was just hoping some of you could give me some ideas for good brushless esc's that I might be able to find used on ebay. Preferably something that can run down to at least a 7.5T motor. Also I was wondering how big a difference sensored vs. sensorless makes and if an older brushed setup would still be competitive. Thanks for any info.

Kyle