I actually think it's free, but very limited on what you can bring in (like catering, alcohol, etc.)
Check this out:
yes its free, it's first come first serve...but they have a bunch of rules. My neighbors got married there in June though and broke every rule and apparently other people have been to weddings where they've broken the rules and it's been okay. We just didn't want to take that risk, it's up to you! The Hall of Mirrors is $1800 to rent which is half the price of a lot of other places around OKC. You can buy your own alcohol and choose your caterer there, also. Hope this helps.
Click on each tool to see a sample.