Our experience with Desert Adventures was great! We wanted to try kayaking on Lake Mead, and they were suggested to us. It was $60 for a 2-person kayak from *10am-2pm (plus the $10 fee to get into Lake Mead). They meet you down at the lake and unload the kayak, and give you that basics (life jackets, paddles). We had a great time (and a great work out), and the price was right. The whole process couldn't have been easier. If you're looking for something fun to do off the strip, give them a try.
* Technically, you aren't getting 4 hours of rental time. They meet you down at the lake, and the van with the kayaks leaves at 10am, so you really aren't going to be in your kayak before 10:20 or so. This wasn't a big deal for us, but it might bother some people. They're pretty cool about it, and would probably give you a few extra minutes if you asked.