Odds of Getting In
It's not getting in to MMA that should concern you; it's getting out (or at least being able to walk out vs. being rolled out in a wheelchair). Any bar with a cage and amateur fight night will let you step into the octagon and live out your dreams—before you get knocked senseless.
Your odds of actually making the pro circuit depend almost solely on your ability to go toe-to-toe and not lose. If you're so good that you win most of the fights you're in, you're pretty likely to make the big-time; if the only move you've perfected is the ol' swing-and-a-miss, then you have better odds of getting into a full-body cast.