Depends on a lot of factors but on average you can expect to pay $90-120 a square foot easily.

Thanks Eva. I expect to pay just want a nice basement and don't really want the pre-fab walls, etc.
Basement is dry (waterproofed).

No problem. its a loaded question that varies. I'm assuming you'll want to add a bathroom and possibly a small kitchen. The space needs heating and cooling unless the mechanicals are in place. Then a bedroom with your finishing touches. It's just math:)....good luck

Bunch of fruitcakes^^

You may want to do a search in the Houzz searchbar for basement remodels (or other similar terms) and look at pictures to get ideas. You can also do google searches.