$1500 could get you lots of goodies if you don't get anything brand new, or could barely get you exhaust, EBC and DP if you get everything new.
Here's what I'd suggest for BPU if you don't mind getting stuff used but in good shape:
1) used exhaust $300-$500 (plenty of Greddy PE, Thermal Research Development, and even Apexi N1 around this range)
2) used downpipe (DP) $125
3) used BCC (boost cut controller) $60
4) used EBC (electronic boost controller) $150-300 OR if you want to save some here, you can go with a MBC (manual boost controller) about $25-60 used or $70-100 new
5) used boost guage $50-150 depending on how fancy it is
Really this is all BPU is, and you'd be about $1k at this point (little more, little less depending). With the rest of the money, you can even get a air/fuel controller for less than $200 that'll get you even more power with tuning. You'd need to save up for FMIC unless you can get one dirty cheap.
The last thing I'd say is definitely get a hose techniques silicon hose replacement kit for your Supra. The stock hoses are crap and deteriorate drastically over time unless properly conditioned (which no one does). You'll be amazed at how much more reponsive the engine is after hose replacement. You'll also learn A TON about the engine by going through this time consuming exercise.
Get my drift? Same thing with say suspension parts. PM if you have more BPU questions as I may have parts that I'm getting rid of
