another thought is go to a reputable dealer (not a department store) where you can talk to the owner, tell them your condition, and discuss returning the treadmill if after a few weeks, if it starts giving you pain. Then you could either return it, or switch it with a lower-impact device, such as an elliptical trainer.
Get the best quality you can afford, I've tried to go cheap on some exercise equipment, and it never worked. Those all-in-one machines they advertise on TV, well they were in many pieces after a few months. And the quality of the motion, especially on the elliptical trainers is important, you don't want them rattling & scraping. Treadmills break down a lot, too, expect that you will service calls to your house for replacement parts, unless you are handy, and willing to look up on the internet for those parts.
BTW, how cold is your pool temperature in Las Vegas? I am determined to start swimming here this spring when the water reaches the roasty-toasty temperature of 68˚ That is pretty much when all the big pieces of ice have melted, just a few scragglers left. At least I have a hot tub to run to when I start shivering! We are thinking about getting a set of those floating balloon-thingies, that are supposed to help the sun increase the warmth in the pool, maybe that will help to get more usage this summer!
