best advice I can give you is to sell your Supra and pick up one that had a GOOD 2jz swap with a single turbo. Pick one up for between 6k to 9k and save yourself a ton of money and headache.
The key is... as rustfree as possible (the body can cause you headaches later on if you dont know what to look for.. ), straight and decent paint. Anyone can do a swap... few can do it properly and cleanly.
I am on my 5th year of buying parts and upgrades for my Supra and if I could do it all over again I would have bought a complete Supra, saved myself 20-30,000 bucks and just maintained it and improved it over a long period of time (just to personalize it).
If your going to run against a MKIV though, make sure your brakes are solid first... then make sure your suspension is in excellent condition. Stupid people drive as fast as these cars can go without checking if they can stop or stay on the road. Then make sure you have rubber on the car that can hold the road at high speeds. Once those are taken care of then you can look at upping your power.
7MGE wont do it though, you have to swap to 7MGTE or a JZ variant. That means wiring, possible transmission changes, fuel pump upgrade, and a lot of other niggly things. If your a strong mechanic with a good understanding of the car you may be able to get all of this done for 3000 - 6000.00. If not.. think higher... lol.
Then your injectors and deciding on what type of engine management you want.. standalone, piggybacks, etc.. etc... a stock MK3 isn't up to holding its own against a MKIV for obvious reasons.
You will read a lot of stories about excellent builds and you will notice that they do not discuss costs generally speaking. I did all my bills last week for over 5 years and consider myself lucky that my insurance car is covering my car for 40,000.00. as it sits right now. Once the new appraisal comes in, it will probably only be insured for about 30,000 'ish... (if I'm lucky) but if I were to try to sell it.. I would be lucky to get over 10,000.00. (not many will shell that type of coin out for a MK3). Luckily, I have no plans on ever selling my baby. However... I have already raised 6 kids, have 4 grandkids and can afford to be a little stupid on my "parenting reward" that I passed up in the 80's....
Lots of props for wanting to do it, but realistically??? Your not thinking straight.