Sounds like a sad situation. I'd figure up what the cost would be of fixing it versus the cost of selling it outright and getting a different car.
If you can do the work yourself, getting the head redone and head gasket changed would likely cost around $500-1500 depending on what actual parts were needed and etc. If you had a mechanic do it, it would likely be a lot more. If, as you say, it is simply the head gasket, I would redo the head and gasket before putting a used engine in, as you have zero history on any used engine. Different people have different opinions on that, but being a mechanic, I've seen only a few used engine swaps that didn't have problems. We do not offer them at our shop, though there have been a few times when a customer brought their own engine and asked us to install it... I've seen broken rings, cracked pistons, spun rod bearings, bent valves,failed injectors and all on those customer supplied used engines.
The other option which may be the best in your case, especially if you do not have the mechanical skills to do the head work yourself, would be to sell the car as is. It sounds like it may still run, but loses coolant? You can likely get more than scrap value for it, especially with the current market, then I would sell the accessories separately. Then you can use what you get towards another car.
All that is simply opinion based on my experience, and should be taken as such.