Legal Question in Business Law in California

His manager legally bound him to the terms of the contract. You have enforceable rights against him, and could pursue those rights. Maybe a stiff letter from a lawyer will get him off the dime.

Sue him.

Don't write your own contracts anymore. And don't cut other people's hair.

You don't provide enough information about your event or the other details of your situation to provide a very good answer. The simple answer "sue him" was probably as good as you are going to get with the lack of detail you provide. You may have breach of contract damages, you may have a right to specific performance, you may have other rights and claims, but without more information, "sue him" is about all we can tell you.

You could sue either upon actual breach, i.e., when you show up on the appointed day and are refused possession; or you could sue in anticipation of the breach because the owner has firmly repudiated the contract. Your damages could be either the $700 you paid, or the cost to rent a substitute space, or perhaps your loss from being unable to put on your event, if you can prove monetary loss. Sounds like a decent small-claims case. I'd be concerned that the owner may have a defense based on some problem with the contract you wrote, however.