When I was in college, the house we rented had a room in the basment. I was there for two semesters and when I moved in in May, it was horrible. The walls were wet it was so damp down there, I had to sleep with my bed in the middle of the room for a few nights until I could get it to dry out with the old dehumidifier from the landlord.
I went out to Sears and bought one of their Kenmore dehumdifiers. I don't remember which size I bought, but it was mid-range. I think I kept it at around 40-50% and it ran ALL THE TIME in the summer. I'd have to empty it two or three times a day. I finally got an old hose and ran it right into the floor drain of the basement. It continued to run like that all summer and into the fall, only in November-December did it not run 24x7
It actually did a pretty good job in an area about the size you want to dehumidify. The goal was to dehumidify my room, but I kept it sitting outside the door, so the whole basement was comfortable.
I'd check with Sears. I think I paid $100-200 for my dehumidifier and it was worth every penny.