BPU can be had for about $1000 ... which would be Downpipe, Exhuast, Intake, BCC, and Turning up the boost... that should be around 400 RWHP give or take a few.. all supras seem to dyno a little differently than one another.
After BPU you can start adding things like a Front mount intercooler... which for BPU levels would probably be around $1000... then cam gears, probably $300... etc etc...
BPU++ cars are anywhere between 400 and 450rwhp usually.. although depending on what mods you do.. could be higher even on stock twins...
You can get a Supra into the 450RWHP range for under $3k depending on what parts you decide to go with, it can even be done cheaper if you really work hard at it.