I've got one which doesnt get much use but when it does it works great. You have to lock the brake on the back casters manually.

 

its about 200 to 250 it doesnt really pay to buy one if you dont work a lot on trucks if being a mechanic as a living i would . just buy a ladder the same hieght at home depot its cheaper a little peace of ply wood the size of a car creeper you could wire tie it to your truck for saftey and a old sofa cushion on top youll feel like your laying in bed your good to go

 

Being a large lad I can say the edges on the top kinda dig into ya, but it does come in handy.I never locked the casters as I was able to pull myself around if I need to move but thats just me.

 

I use a small painters scaffold without the top bar, ya can pick one up for less than $100.00, and they fold together for storage...
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66866

Harbor Freight $89.00

 

Love the ingenuity , but I'd like to see a picture of how you make that actually works as well as a topside creeper?

 

Only way to go . Makes working on the truck much easier . not to mention not messing up the fenders , grill, etc