First of all, I do not recommend a UMAT tutor. It is said that you cannot study for the UMAT test, and through my experience I believe this is in many ways true.
The reason why I do not recommend a UMAT tutor is because no one really knows the "proper" way to handle the test, and by listening to someone else tell you how they do something, you may be confusing yourself as what you should be really doing is figuring out your own strategies to tackle specific types of problems that come up every year in the UMAT.
For this reason, I think purchasing a program (I would recommend MedEntry, it's probably the most reliable and similar to the real thing) MAY help you develop the skills and techniques that may enhance your performance, but isn't particular "necessary" to do well. Many kids at my school did well with no training whatsoever, so you can do well without buying MedEntry.
Oh and also, by enrolling to undertake the UMAT test, you're provided with one free copy of a sample paper. You can also purchase another sample paper for $20, so I would recommend using these two tests, and potentially even analysing them carefully, as they are released by ACER (the company that like does everything for the UMAT) and thus these questions are likely to be most emblematic of the questions in the real exam.