they can take a fair amount of abuse on the stock ECU, it's got the safetynets built in to prolong the life of the engine. When you put in a lower-end ECU like a powerfc you lose all those safety nets, and it doesn't take much to ruin a bottom end without them. A complete new bottom end is ~$2400 from toyota RRP, add a gasket kit and head studs and you could get away with repairing the car under $3K with DIY labour