There are many companies that offer these services as a do it for you. I would recommend you look at a local business vs the services that are offered on line. I am in the LA area and just set up a corporation using the local resource. If they are legit, they will all charge within the same price range. I would look into the LLC vs a CCorp. If you wish to do it yourself, the forms and procedures can be found on the State of California's website. Nothing too complicated, but the process is time consuming.

With many years of sales and sales management, I can tell you that people buy from people they like. So, you need to look at your business model. Is your existing Sales person telemarketing or out in the field making his presentations and calls and demonstrations? If you are currently using inside sales, then you can hire someone in your area to work the East Coast. If your business model is in the field, then you will need to hire someone that lives on the East Coast. And if that is the case, then I recommend utilizing an agency which will bring you a higher quality candidate.