Sit down driving games like everything else, are pretty much all over the place. But it seems like $250-$300 is about right for a fully working older one. A lot of them seem to go around that price. Newer ones go for WAY more. Dead ones go for WAY less.
I am still bitter about the Roadblasters cockpit that I missed getting. They had just switched auctioneers, and I couldn't understand a word the new one was saying. I THOUGHT I dropped out of the bidding at $150, but it turns out that I dropped out at $50, and it went for $75. It worked, but had a video ram problem.
I also dropped out of the bidding at $250 for a Turbo cockpit which went for $275. I REALLY wanted that one, but no way was I going over $250 when some of the 25" driving games were going for that. Plus I already had an upright Turbo anyway.
But, really. Prices on sit down drivers are highly influenced by how many of them are there, who is buying, the weather, and when they decide to auction them.