I'm sorry you are dealing with this. I would recommend that you contact your lender to start with. See what options they have for you. The new Stimulus deals include options for loan mods and refis without having to go late on your mortgage. As soon as you are 30 days past due, your credit will be impacted.
As far as what you will be asked to pay? Every situation is different. Some loan mods have an upfront payment, some don't. It's very individual and there is no way to predict.
Last point....if you do decide to pay someone to help you....make sure you hire an attorney and not a loan mod company. While there is no way to predict individual outcomes, an attorney is answerable to the California State Bar and will most likely not turn into a scam. Be sure and check them out first...and contact the Bar website to make sure there are no complaints against them.
Good luck with this...if there is anything I can do to help you...I'm happy to!