When we bought ours (about a year ago), amazon had the best price, especially with free shipping and no tax. We did buy one from Walmart first, to make sure it would fit OK in our cars. It's fairly easy to take in and out. The cupholder and cubby holes have been the biggest pluses for us.
We just bought a Nautilus from Amazon for $144 (free shipping w/Amazon Prime) - that was the best price I found. It is the same price at walmart.com with .97 shipping.
Re: Best place to by Nautilus (or other booster)?