I really don't like the prep courses, i went on one and the information they provided was not worth the money spent. It's not the cases of people doing well with prep courses that should sway you, it's the significant number of cases of people who do poorly despite going on these courses. Buy the Acer question booklets as they give the best insight into the UMAT. The courses are full of bullshit (especially interview preparation) and the prices range from unreasonable to extortion. MedEntry provide the same material every year, and their tests give you unbalanced feedback on how you will perform on the real UMAT, as the percentages are derived from medentry student performance. Med Entry is one of the better ones, but ulitmately you'll still walk into the UMAT blindly for the most part.
Look for some of those MENSA quiz books with shape problems in them, they can help and are only around $15.00 - $20.00 each