Slo_crx1

I run EcuFlash on the oem ecu. It's honestly the best way to tune stock ecu Evo's/WRX's/Sti's. On evo's people have run it on setups making well over 550awhp on the stock maf, and now there are patch codes being tested (they work, but not fully tested yet) that allow removal of the stock maf and swap over to the evo 8 jdm 3bar map sensor. Think of it like Crome, but on crack. Look for my thread on it in the engine management section to get a brief overview.

TorganFM

How much do stock wrx ecu's go for? I might go that route instead of MS if I do a Subaru swap.

Slo_crx1

I honestly don't know an exact number, it tends to fluctuate depending on model year. Keep in mind that EcuFlash will only do MY02+, so if you do a subie swap you'll probably need every piece of harness (inside and engine bay) to get the ecu to work properly. On the plus side, you can disable all the cel codes. Check out my EcuFlash thread on here for info on the subie setups.