And I'd like to put it on eBay.

From the research I've done, a copy of this game is valued at between $80 and $100.

Would the fact that it has only one piece missing (a prize card) steer bidders away, or is this slightly-imperfect game still reasonably valuable?

This is a subject I'm pretty familiar with, and I would gently suggest that your research is flawed. You may have found a reference book or two that quoted such a figure, but the truth is that when the game turns up on Ebay, it just doesn't go for that much. I think there have been people here who've picked up copies for less than ten bucks.

It's rare, yes. One of the rarest. There just aren't a lot of people around who want it. The fact that a piece is missing certainly doesn't help matters, but it's impossible to say whether you might find a buyer out there who doesn't mind as long as the box looks good. If you're really lucky, you'll find two would-be buyers that start a bidding war.

If you're not comfortable letting it go at any price, put in a reasonable reserve, something you'd be happy with (I'd suggest $50), and cross your fingers.

I'll second the home game expert's comments. As you can see here, last year I picked up a complete copy of the game for $8. It wasn't quite in mint condition, as it was described, but it was in pretty good shape for its age and, again, complete. I wouldn't expect to get 10 times that much for an incomplete version.

In the spirit of full disclosure, I should add that I actually paid $100 for mine, about twelve years ago.