Again, the FREEWHEEL that you have is a different type of mechanism than a FREEHUB equipped bike that uses a CASSETTE. They are NOT interchangable. Yes, you can get a 7 speed cassette and a spacer, so you could possible use that wheel, although the dropout spacing for a 7 speed freewheel equipped bike is probably 126mm, instead of the more modern 135mm. If that frame is aluminum, then it may be difficult to squeeze a freehub equipped wheel in there. And just because a bike seems expensive to you doesn't necessarily make it worth putting any money into for upgrades.