Can anyone suggest a Kayak trainer that is reasonably priced. Possibly under $500?

are you asking about a rowing machine?
If so, there is a German company called Kettler that makes very good rowing machines. I have a Kettler Kadet that I have had for over 7 years and it allows for rotation so it keeps your core muscles in good shape, and it has never worn out yet. I think it was around 500.