There is not much of a market for 1977 to 1985 924s right now. I bought a 1977 1/2 924 for $825, and it needed a lot of work (still needs a little more). I have probably put $2000 or so into it, and if I were to sell it today, it may get $2500 or $3000 if I am lucky. And that's with a custom 7 speaker sound system w/sub, new brakes all around, new fuel accumulator (old ones fill w/dirt and cause havoc with the fuel system), fuel pump, fuel filter, new head, new water pump, new seals all around, refurbished fuel distributor, cleaned fuel tank, and the interior carpets ripped out and cleaned.
My guess as to what you could get, assuming from what you told me and what I've seen on other 924s is going to be around $300 to $700.
Cars are a losing game. If you drive a new one off the lot, $3000 down the drain. If you buy an old Porsche 924, it's going to cost you more than it is worth. That's just the way it is. Luckily for you, you got one at a decent price.
Before you put it up for sale, why don't you fix some of the problems? Get the body repainted or fix the interior. It's the small things that count, and usually for this car there are a lot of little things.