Its usually length times beam times a factor which depends on the surveyor. Travel costs can be added.
Everything is negotiable.
Be sure that you choose a reputable surveyor that is used to surveying wooden boats. Make sure that you know exactly what you are asking for in the survey. Hull only, full condition etc etc. Surveyors usually don't comment in detail on engines etc. They also won't comment on the rig that they can't see close up!
It depends on the surveyor but I think usually, yes, the price is a function of size. I recently paid about £250 for a survey on a 25' boat so I guesss you should expect to pay >£300. You may find http://www.ybdsa.co.uk/SurveyFAQs.htm useful.
You can do a deal on the survey though which most surveyors are OK with: if anything serious is found during the survey then drop out at that stage. You can either be present or discuss by phone. The surveyor doesn't write anything up so saves his time and you get a cheaper survey. You just pay for what you get.
I had a boat surveyed like this once & got a call to say there were some very strange things. He stopped at that and despite me making several calls I never got an invoice. That's what I call service!!!
Survey fees vary enormously: I’ve seen charges from £8 per foot of length to a calculation of Length x Beam x 1.5 + VAT. For a 32 footer with a 10ft beam, this means anything from £256 to £564. I would suggest that anybody charging less than £10 per foot for a pre-purchase survey is unlikely to be a full professional, and almost certainly isn’t carrying the cost of professional indemnity insurance (circa £2000 a year, even for a surveyor with no claims against them).
In addition to making sure they are a wooden boat specialist, make sure the surveyor you engage carries full Professional Indemnity Insurance (ask which company: expect Galatea, as they appear to have a virtual monopoly), and is a member of a reputable trade organisation such as the International Institute of Marine Surveying (IIMS) or Yacht Designers and Surveyors Association (YDSA). Say that you are interested in coming along at some point during the day, so would like to know the hours he will be there: a good surveyor will be fully occupied all day on a wooden 32 footer (think how many pieces of wood there are, all of which should be inspected).
Ask how long after the survey the report will be sent: you will want it quickly, but be wary of anyone who states they can draft, proof-read, correct, print and bind a meaningful report (about 1 page per foot of length, including relevant pictures) in less than 36 hours. Many surveyors will supply an example survey on request: from this you can see how thorough they are, and you can make your own mind up.
Also, beware additional costs:
1. As the prospective purchaser, you will need to pay to have the vessel hoisted out of the water and scrubbed clean, if it isn’t already.
2. If you are particularly concerned about the engine, factor in the cost of a full engine survey by a specialist on that particular make.
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And if you want the survey to be absolutely complete, i.e. the mast/rigging, you will also need to pay to have the mast unstepped. A surveyor will not comment on the rig without close inspection, and if the insurers have any doubt they could put a clause in the policy.
Don't forget, if you don't purchase you have to pay to have the boat put back exactly how it was before you started, i.e. mast stepped and in the water.