Get a second or third bid. There's no reason to go with the first company.

On the other hand, I'd believe the cost isn't too bad. If I were cleaning up sewers, I'd want a hazmat suit. And the wood is soaked with sewer water; they should be replaced.

Was the backup due to you or something else? It is likely the Condo association's insurance policy may cover some of the cost. And if not, your homeowners might cover some of your share.