How about a Momo Start? It's fiberglass, so it's inexpensive, and it's FIA certified, so no back brace needed. I had one in my Rabbit and it was slightly snug (5'11", 200lbs) but might be just right for you. I think it was $270 shipped.
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I would think that's the way to go. I have a Kirkey Intermediate (with most of the the rib protectors cut off), but I'm a fairly big guy in a little car. If you've got a little room to work with get something with a little more padding.