This is the same car that has been standing since 1980? I believe you've not run the engine yet?
I think you're worring too much about costs on a theoretical basis. I'm all for planning and budgeting, but you're short on information to do this.
Running a car like this is a hobby. You should only spend what you can afford, and if you can't afford it, don't spend it.
I think you should concentrate on finding a mechanic you trust to do a proper survey on the car. You know you need sheetmetalwork, you think the injection is suspect, now you are worrying about an engine rebuild.
A lot of braver souls would have flushed out the fuel system, cleaned the plugs, connected up a new battery and turned the key! Then you worry about injectors, big ends, valves etc.
Old cars do need care and consideration, but sometimes you've got to remember they are machines, not fragile antiques!