Howdy! There's a lot you can do with $50K in a Supra - I'll give you some insight based on my buildout.
In the motor department - the bottom end is plenty stout, so just look into a good single - I would say a T-63,66, an HKS T04R, or a Greddy T-72 is a great setup (lag is very over-rated on the meduim-large turbos) - this with fuel, gauges appropriate electronics (VPC, EBC, AFC, etc.) and a good FMIC (I'm running the HKS Type-R). Let's say about $10K-12K.
You'll need a beefier clutch, or a high rpm stall - for the clutch the RPS single disc setups seem to be holding up well, or a TRD twin disc, also a good route. Call this another $1500 or so.
Suspension - you can save money and go upgraded springs/shocks, or get into hard core road racing setup using coilovers - TRD swaybars, and some good strut braces (I'm running TRD front and Cusco rear) round it out nice. Anywhere from $500 - $2000 depending on the options here.
You'll want a wheel/tire upgrade - 18" are good match, anything by Racing Hart, Volks, Fiske, etc., are outstanding - A Volk TE-37 is a great wheel for only about $300/ea, all the way up to HRE for a good $1K each! Call this $3000-$4K with good tires.
You can leave brakes alone - the factory brakes are outstanding - or just upgrade the lines, fluid and pads for cheap, and have a nice upgrade in the $300 range - I'm running AP/Stillen 13.8" with 6-piston calipers that will almost brake the passenger seat during hard stops! Something like that, or from Baer, Willwood, etc., will set you back about $3000.
Cosmetics? Paint a good $5K (for a high end job) - various spoilers, nose clips, side skirts, etc., can run anywhere from a RMM fascia for $500, to a complete Top Secret kit for $4K - and of course, radical wide body conversions (but that would definitely push the car out of the $50K for upgrades range).
All sorts of other things might fit into that budget - seats, interior parts, rollcages, etc. - you could drop $10K on the sound system alone! (I only spent about $5K in that department, but for an excellent sounding Eclipse/MBQuart setup). Seats, white gauges, polishing (I probably have $3000 worth of polishing).
There's also a sizable difference in the cost for labor - if you're a do-it-your-selfer, vs. paying - or maybe a mix.
*OR* find a completely done up car - a buddy of mine actually sold his 94 to buy a completely done 94 - it's easy to get your money back out of an existing car.
As a final FYI - my car is always for sale (thinking about a new project) - you can see pictures, info at the links below - not a formal "For Sale" - just always willing to entertain offers