Cost to the dealer is very similar to the Vista without SpAudio, so when you are comparing his prices, the Aria will probably be right in the range of the Vista.
What is your dealer including for the $8900? If he is including some steps, a cover lifter and star up chems, that is a good price. You might be able to get a little more off, but if he is at his bottom line and won't budge, then you're probably there.
The Aria is a nice spa. I have wet tested it and liked it very much. The stereo is decent and works well. The lounger is well-designed. I didn't float at all and I usually do.
Good luck in your search.