Well, I only have two cans so far, but from what I've seen, at or close to MSRP isn't all that uncommon around these parts. It doesn't seem all that competetive a market - there's only a couple of dealers within driving distance that I'm aware of than stock any cans, and among those very little product overlap. Therefore, they're pretty much free to charge what they want. You may be able to find something out of state a bit cheaper, but you're talking a longer wait (assuming the local dealer already has something in inventory) and the cost savings is probably going to wash from the transfer fee you'll need to pay to your local dealer anyway.
While the tax is getting to be not so much of a hardship anymore, the process is still indimidating to most folks. Therefore, I think civilian sales are still relatively low volume, which means that the average dealer probably isn't getting much of a huge volume discount anyway. Couple that with the extra work involved, say vs. a title I sale... If can isn't going to bring a greater profit margin than a title I gun and you aren't going to sell many of them, I wouldn't see much reason to bother, as a dealer. Which could perhaps be why there doesn't seem to be that much competition in the market, and we go round and round....
Yes, while the tax may legally be the responsibility of the transferor, for all practical purposes, that never happens. And if it does, it is only because the seller has already adjusted the base price to include this. Also, in your original post, you mention the first transfer tax. As long as you aren't purchasing the can from a non-licensee, there is only one tax. Which is why it is pretty much pointless to ever buy a used can.