My neighbor has a kayak, I couldn't tell you much about it other than he told us he bought it in the early 2000s, so I believe it's at least 9-10 years old. A friend of a friend has a kayak and she got it for around $15k I believe. At a dealer outside of Chicago. I was quoted around 18k, down to 15k on a clearance model. I personally wouldn't want to spend much more than $12k at most.

Assuming you get a standard agp, lets say the kit costs around 3500, then you might spend another $1k on installation. Putting up a deck could set you back another $1500. Depending on the city ordinances if you need to put up a fence around it that would probably be another 1k-1500. This could take you up to 7500-8k. Still much cheaper than 12k, and way less than 20!

Keep in mind you can get an expandable liner and have a deep end created for your agp. Kayak isn't needed to get a deep end on your pool. Many people have gone with doughboy expandable liners and they even warranty their pools to be buried, I've seen many sunken 2'+.

Oh, I also noticed my neighbors kayak came with a small sand filter. Equipment would be another thing to check on w/ kayak.