MechDiver once bubbled...
I'm evidently not getting my point across. IF the purpose of the class is to teach you how to use some type of equipment, then what would be the purpose of making a substantial equipment purchase beforehand, that may or may not be correct (someone said stroke), so you can "practice" 
I understand your point just fine, I just don't exactly agree with it.
So you dont want to spend a bunch of $$ on doubles to practice with, that is understandable.
BUT there are alternatives.
As far as buying equipment beforehand, one of the things I do is communicate with my potential instructors exactly what gear I have and exactly what gear they require. Most of them will have any gear you need available for use/rent, so that will keep you from having to spend a lot of money on gear until you know exactly what it is you need or want.
As far as doubles go, there are alternatives. Buy just a set of bands if you want, and double up a pair of AL80's. You don't have to manifold them together in order to get used to the bouyancy characteristics of them. And I am pretty certain you can find two AL80's somewhere to rent/borrow. So all you would be out was the cost of the bands, and you can prolly Ebay them pretty easily if you decided doubles werent for you. If you can find some steel tanks to do this with, it's even better. I'm also not saying that you have to be 100% proficient with them. But a little familiarity goes a long way to keep you from floundering around while trying to learn other skills in a class setting. (plus it's not nearly as embarrassing that way)
Even if this isnt exactly the setup you will be using for your course, it will allow you to get some experience.
I also disagree with the statement about "if the purpose of the class is to teach you to use them." As I started getting into more advanced types of diving, it was pretty well expected that the student already have SOME familiarity with the equipment PRIOR to enrolling in the class. If not, expect to spend a few extra days and a few extra $$ while the instructor "babysits."
I can fully understand and sympathize with concerns about spending large amounts of cash to find out something isn't for you. I was fortunate in the fact that I was able to borrow a set of doubles to practice with prior to my cave class, and I was able to use that same set for my class. Believe me, it made a WORLD of difference.
Just keep in mind that there are alternatives to be found if you really want to.
But the most important thing to remember, is that what works for me, may not work for you. You have to do it the way that YOU feel comfortable.
