It all depends on how the person(s) before you have taken care of it. I really don't understand why so many of them get to the point they are and the next person has to go through so much crap to get it back to where it should be.
Obviously as a car gets older parts will fail and need to be replaced, but the cars definitely CAN BE reliable. The cars themselves are made well, durable, and reliable. It's the owners/previous owners that do not/did not take care of the car that mostly give these Supras the bad reliability reputation. My dad is the original owner of my 92. In the 15 years my family has owned it, it has been down a total of ONE week. ONE. This was when the headgasket was going bad. Get the headgasket fixed CORRECTLY and you will not have a problem with it. However, please keep in mind that is unfortunately is not the case with the majority of them.
The best way I think would be to just save up, wait, and find the one you want and one that's in great condition the first time. Research some of the problems and experiences of others to get an idea of what to look for. This Web site is a great place to learn. Some of the cheaper ones may sound good, but keep in mind you may be spending more than some of the more expensive ones in repairs, maintenance, etc.
Try to find one that has been taken care of- service records, smaller number of previous owners, and close to stock condition always are a plus. But the maintenance of the car is the most important thing. And remember no matter how great shape the car is, expect something to fall apart or fail due to age so keep that in mind with funds available for the unexpected.
Supra's are great cars- find one that has been taken care of and you'll enjoy it. I don't ever plan on getting rid of mine.