It is a doable project although you may need some help. You might have a lot of digging to do. $75.00 tells me there are some parts missing, holes in the liner, and the pump and filter needs expensive repairs.
I hope it is set up and in use so you can see and take pictures of the setup and make sure everything works. If it is laying in a pile in someone's shed somewhere, then let the buyer beware. Good luck.