1. Newer kayaks = more comfy, better ergonomics (esp at your height/weight), good prices
2. Do some online research of the new/newer kayaks
3. Demo as many kayaks as you can when you come to Colorado
4. Decide what kayak(s) you like the best
5. Keep an eye out for used ones, including older versions, similar versions (Liquid Logic FreeRide vs. Jackson 4Fun), etc.
a. Keep in mind what you'll use the kayak for. While a river runner/creek like kayak might make class III real easy, it may also mean class I/II runs are boring. A free running kayak may challenge you on class III, but it could be a blast on class I/II rivers.
b. Look at the River Runner & Free Runner kayaks on Colorado Kayak website. Lots of options, most of which can easily be found used for less than $500.
c. When you come out to Colorado stop by Colorado Kayak in Buena Vista - they always have several different types and brands of kayaks to demo. The shop isn't far from the river and in one day for the price of one rental you could easily try out five or six different kayaks if not more. In addition, when you run into people on/off the river don't hesitate to ask to sit in and/or paddle their kayak.
d. Get to know the kayak models, the # of generations, and the differences between the generations, etc. For me, the difference between the 1st and 3rd generation JK 4Fun is HUGE. Whereas the difference between 2nd and 3rd generation Pyrahna Burn may be more subtle and less important to you vs. a pro that paddles all the time.