Is you car the early 924, or the 924S? On the early (Audi-engined) 924, a timing belt is not a big issue. However, on the newer 924S, it has an "interference" engine, meaning that the valves collide with the pistons if the timing belt breaks. If this is the case, the repair cost will exceed the value of the car you described.
Another concern with the 924 is the Bosch K-Jetronic mechanical fuel injection. While this system was well-received when new, a twenty-plus year old system is likely to take some maintenance by a knowledgable mechanic. Also be advised that these systems do not like to sit idle for years, so if this is the case, be prepared for some parts replacement. The other option is to convert to Weber carbs (which I did), but this is expensive.
There are kits available if you want to convert to an American engine, but again the cost will be higher than the resale value upon completion.
I am in the midst of a 924 restoration myself, and have learned the hard way that you are far better off financially buying a clean, running, driving, car, than repairing one with engine, paint, and body issues.
I suggest that you go to
www.924.org and review the wealth of information there. They have a free "for sale" section if you decide to sell, and a discussion forum if you decide to complete the project.
Best wishes.