If you are looking for more of a game room type area then you might consider only semi-finishing it like I did in our basement - it was inexpensive and only took a few weekends to do it myself.
1) Painted the concreted floor with special epoxy paint
2) Put area rugs on the floor. With the area rugs and painted floor if there is ever a water leak then it will not be a big deal.
3) Repainted the concrete walls with sealing paint, and then made storage areas with shelving about 18" deep with sliding doors all around most of exterior concrete walls. This leaves the concrete walls accessible so that if there are any leaks or moisture it can be seen and dealt with easily.
4) Drop ceiling with acoustic tiles
5) Hired someone to do the wiring.
+ add a proper ventilation, we had to fix ours in the end and got a lot of problems not installing a fan
in the first place
It is nothing fancy but it is fine for kids to hang out in for a few hours at time. Otherwise it can be used as a home theater.