Joey you are looking for a smallish houseboat with your criteria/budget. Drop sleeping 7-10 people and you can get into a well found older power cruiser that could sleep 4-5 in reasonable, short term comfort.
Some of the older Land-n-Sea style trailerable 28' houseboats sleep 8+ people and are cavernous inside. The following link will take you to the blog of a friend of mine named Jeff who owns one and cruises it extensively. Not the most attractive boats in the world but they are very good at what they do.
As to operating costs, that's like trying to nail jello to a tree. Some folks spend very little others of us spend our share plus theirs too. All depends on how yachtie ya want it to look and what size/where you berth it.
Good luck in your search.
Edit: meant to mention 36' Gibson houseboats. Dime a dozen and can be had for anywhere from $8,000-$25,000 depending upon age/condition. Tons of space and great on inland waterways.