Don't choose a surveyor on price alone.
Of course you need to know up front what the cost of the survey will be, but it could be a case of "if you don't pay now, you'll pay later." That bargain-basement-price survey could cost you in the long run should the surveyor miss some important fault on the boat.
If problems are caught before inking the deal, you have the option of renegotiating the price or getting faults corrected before you take delivery of the boat. While there is no guarantee that you will get more from a more expensive surveyor, as in all things, you typically get what you pay for. Prices are generally around $20 to $22 per foot, but if you're quoted $12 per foot you need to ask yourself why.
Surveyors often get concerned when a client asks for a cheap survey because "it's only for insurance." Most surveyors are professionals and want you to be happy with your boat and ensure your safety on the water. In return, you want him or her to spot any deficiencies with the boat. Surveyors need to be able to stand behind their work (possibly even in the courtroom), and doing a "light" survey doesn't help anyone. Most surveyors have a set fee based on the size and type of boat, the type of survey, travel costs, and so on.
By all means ask how much the surveyor charges, but don't wait until the day of the survey and then try to start negotiating the fee. You have the right to back out of the purchase up until your contract acceptance deadline, which is often at least several days after the survey date. If you change your mind about the boat after the survey is done, the surveyor still has to be paid. Most surveyors expect payment on the day the service is completed. Surveyors typically won't send out the completed survey report until they get paid. It's the surveyor's version of "no cash, no splash."