If you really want to go this way, I'd look into an old box truck. Actually designed to carry cargo, and probably has a diesel. We bought one for work, and it would probably make a cool car hauler. It's a 16' Hino, w/ a high box that's big enough to stand up in. To me, biggest issue is getting the car in. You might find one w/ a lift gate. To me though, there are a couple of downsides. Most don't have a side door, but even more importantly, most only seat 2 people. I'm also not a big fan of vehicles where you sit out over the front axle!!! Should do 60 - 65 on the highway (but that's probably about all) ok. The one we got was a '98 w/ 225k miles on it (properly maintained, they're probably good for an easy 400k. I think we paid $6500 or so for it.

As far as one of the coolest car haulers ever, anybody that's been around the Northeast since the mid-90s, has probably seen the converted fire truck of Entropy Racing. It was an old American LaFrance ladder truck that had the ladder and the turn table removed, and ramps built on top. It was mostly used to haul Spec Racers, but I've seen other cars on it. Fit two cars, and would pull a dual-axle open trailer behind it.

AFAIK, Charlie still has the fire truck and it's still going strong. Oh yeah, he used to drive the cars up on it! :119: