Welcome, and i promote your interest in going to a Supra. I just purchased mine a few months ago, a 97 Supra TT with less than 60,000 miles on it. I payed just under $30K for it. That is almost stock though. I prefer stock for several reasons; you can do your own mods, and you know that someone didnt just ghetto rig stuff. Mods for a Supra will defiantly be cheaper then mods on a BMW. For a good FMIC you would be looking at between $1500 and $2000 depending on brand, and for turbo's; it depends on a lot of factors. If you want single or twin (sounds like that is what you want) prices can vary greatly especially if you want to upgrade to bigger TT. You will just have to look around the net. Hopefully others on here can help you out more on prices, and you can check out this website for some good upgrade parts. Good luck.
http://www.mvpmotorsports.com/merchant/supramkiv.shtml#