Well what toxic said is not exactly correct. If you have the money you can walk right in to most all of the gyms and train at a high level heck Jacksons has their fee's right on the website.
It wont take long for the coaches to place you after you get there and most gyms put you through a evaluation of your skills so they know where to place you.
You're not going to walk in and start rolling with Jon Fitch but if you have the skills and ability its not going to take long and you'll be in with people of your skill level.
It's all about the cash.