Hi Scott. Welcome to the group. Some sites, such as aopa.org and I think also cessna.com, have some advice on how to choose a school that's right for you.
As for the Medical, yes if you have any conditions you think might be a problem, it's best to get the Medical before starting training to make sure you'll pass. Depending on the nature of the specific problem, you may want to just see your regular doctor about it, rather than some special company. That probably would be cheaper. In my case I was unsure of my vision, so I went for an eye exam and got new eyeglasses which helped me pass my medical. The eye doctor can check for color blindess and other vision related issues. If your condition has to do with other things, maybe your regular doctor can adjust your meds if needed so that when you go to the AME everything will be just right.
Usually the schools can provide a list of AME's in the area. So maybe you can start by visiting a couple of schools to check them out, but while you're there tell them you want to get your medical first, and ask them if they have a list of AME's.
I hope this helps.

Yes, the cost can vary quite a bit. I paid $125 for a third class. A friend paid $80, about 50 miles away from where I live.