Lotsa jerks on the internet... I'm sure that they make mistakes too, but they'd rather point out others' mistakes. My theory is that it's because they don't get enough sunshine and human interaction--don't take it personally!
I would not pay $200 to get the screen replaced. First of all, Best Buy is one of the most lenient stores in terms of returns. Even if you are not successful one time, I would try again on a different day at a different time of day. Not sure what story you should give them though... probably shouldn't lead with "I dropped it."
If that does not work, then you should be able to make the repair yourself. Unfortunately, 3GS parts are not really on the market for 3rd party vendors right now, so you'll either have to live with it or try it with the 3G screen. The 3G screen should fit, but I don't know if they changed any of the cabling, a la the charger pins. Since that could lead to an even worse situation, I would probably just live with it until you can get 3GS specified parts.
If that time comes there are several vendors, so you should shop around for the best deal, but go ahead and bookmark ifixit, because their teardown instructions are excellent. You can probably get a good suction cup from your local dollar store and a good stiff guitar pick is much better than their case opening tools (at least for the 5th gen ipods). I would expect the cost to be closer to $60-80, so maybe it's not worth the trouble for you.
M@