Is my car repairable and if so how much would repairs be

Heater core went out 3mths after I bought it used. I had to keep putting water in my overflow tank so that I could even drive it. Then about 3mths later a rusty brown color, maybe oil, was in the overflow tank so I quit driving it so I would not do any more damage. We had no money at the time to fix anything or even have it looked at so it has been sitting in our driveway since last fall. My question is if it is even fixable and if not what would be a fair price to sell it as is. The rest of the car is in mint condition.