Well then, all you'd really need would be a length of tube, two end caps and a tray inside the tube to mount the radio, batteries and motor upon. A length of tube will cost you around £10-15, depending on the diameter you need...a pair of end caps from Mark at MMB around £20-25, and a sheet of styrene about a fiver. And there you have the basic wtc for a dynamic dive boat. Add the prop shaft and watertight linkage exits, again from MMB, and you've got yourself a wtc for around £50 ish. Nice, cheap, and effective. A couple of days work should see it completed and ready to test in the bath.