bro,
remapping/rechip is a old style of tuning.changing tuned version chip or copy paste tuned map into current standard version but u need hardware to support the tuned chip or map.
u mean by reflash?atr ecu is like computer can read n run itself wif input parameter such as sensors n blah blah blah.reflash is like format ur pc and install new version of windows to let it run smoother or better.
reflash cost 1k-1.5k.increase of decrease all depends on your hardware.example,ur pc is pentium 3,after format it will not jump to pentium 4 lah.