The Dacor Seasprint is a great little scooter. It is tough as nails and very hard to flood due to it's double 0-ring on the case. I have abused mine for a year now and recommend one highly. You should be able to find one for around $1200 complete with 2 batteries and a shipping container.

A couple of drawbacks of the unit are it's limited battery life, about 20 mins on full blast. But keep in mind that WFO is 40 lbs of thrust. You can get along just fine on the middle speed which lasts about 40 mins. Which brings us to the 2nd problem, you have to adjust the hub of the prop to change speed and it's hard to get it on the middle speed. A throttle sure would be nice.

The control handles are up at the front which means that the standard Mako/Gavin harness does not work. So the hot setup is to put a tow clip on the fan shroud to clip to your crotch ring. This setup is not too good for caves but for wreck diving it is ideal. The scooter is negative and with this setup you can keep it attached to your harness for the whole dive. If you need to use your hands you just let go and the scooter flops down between your legs. When you need the scooter you just kick up one knee and up it pivots into position. Neat!

While you can put the carabeaner directly on the loop but this would constitute a metal-to-metal contact. And you can adjust the string attachment for length to position the scooter correctly. The fitting is a standard blow-boat fixture and can be found at West Marine or similar stores. Make sure you use lock washer or NyLok nuts. I use the carabeaner because I need to be able to clip the scooter off on the anchor line or the hang bar. But you could use a double-headed bolt snap as well if you did not want the adjustablility.

Addendum:

I see that lots of divers have taken a look at these pages. I took photos of the different interpretation of how to do the above and made a page for your enjoyment: