Testmasters is very good, but like you pointed out it is quite expensive. In my opinion, if you are serious about the LSAT, you need to do whatever is in your power to improve your score. If you're able to shell out the money and it is worth it to you, then do it. If you're not sure about it or don't have the option to spend that much, there are certainly cheaper alternatives. It's really up to you. Like you said, there is a lot more prep material in Testmasters, but you have to look at your situation and decide what you want to do.