It actually works out to about 4 - 5" of quilt space on an average sized quilt (lap or child). The bars the quilt is rolled on take up the rest. It also depends on your batting; high loft batting will take up more room, thus reduce your quilting space.
Do some research to find out what a comparable new frame and carriage will cost. If the frame and carriage will accommodate a larger throated machine, then you may want to think about purchasing the frame and table and acquire a larger machine later.
Also, look on Ebay or search for used long arm machines. Then you know what the going rates for used set ups in good condition are.