depends on what year supra it is and whether it has no turbo, 1 turbo or a twin turbo stock. so I can't really help you with price without that info.
If you have the twin turbo supra then you can put 5,400 down on a new turbo system and have 1000hp. But with that your going to probably have to install a roll cage to hold it together and a new transmission.
The best thing you can do is go on a supra forum and ask the guys on the site how much it will cost and what you will have to do.
That inline 6 motor is capable of handling so much power, and the whole car is so well made that you probably won't have to upgrade as much as other cars to keep up with the power. Thats why the supra is such a popular car to modify....