It took more than 4 hours but part of that may have to do with the fact that I had a rollbar to yank out and then reinstall and I tried to do everything "perfectly"...
I got a no-name brand off e-bay. One thing I had to deal with were some extra vinyl flaps that weren't trimmed. I had to call in an "expert" to de-stitch and back-stitch those bits so that everything would fit right. These were where the top mates to the rain-rail and I feared that leaving them would result in a poor seal.
$300 in labor? Hmm. They guarantee no leaks and warranty the install that it will be perfect and not come apart/etc? That might be worth taking them up on.
Turned out that in the end, it didn't really matter so much and after 2 years, the top is holding out okay but I made the mistake of not installing the interior in the back since I was chasing a leak and managed to get red paint to lift onto the vinyl window (I had a towel in there for a while and at some point removed it - big mistake). Oh well. Live and learn.
I guess my verdict is:
Yeah, I did it myself but I'd think twice about doing it myself again even though I know all the gotchas. It's not particularly hard...just time consuming and one or two steps were sort of "evil" in terms of accessibility to something or other. Read the miata.net howtos and see what you think about the job after reading through them.
Make sure you get new "cables" with it. New rain rail probably a good thing...I did some RTV repair on mine that has held out but you never know what you'll end up pulling out.
--Ashraf