I have a blackburn fluid trainer. You have options of mag vs. fluid, remote or no remote... Just make sure it will fit your bike and has enough resistance settings. They hold their value so if you buy one and decide to upgrade it should be reasonably easy to sell.

Re spin classes. I wear a HRM and I find the classes are a great way to work on the higher thresholds. The benefits of training you heart will carry over to cycling even if the moves do not. There is one instructor who has been tough enough to get my HR into the 190s!