You don't mention the type of survey or if the property is residential that is in a rural area. I am not as familiar with survey costs in Maine so my basis is my experience in Ohio.
In most cases, the survey cost is up to negotiation just like any other cost associated with closing the loan. Standard residential surveys are usually around $500 to $1,000 depending on the developed area. This can change in more rural areas where there has been changes to property classifications, sell-off of parcels, and other types of modifications to the property area.
Even though you do not have many potential buyers in the area, is the cost of this survey going to provide any value to any other potential buyer? What is the main purpose of the current prospective buyer by having the survey done? Is there something specific that they are looking for from the survey? How much real interest does this prospective buyer have in purchacing the property?
With some of these questions answered, you may be able to work something out with the cost of the survey and sharing that with the prospective buyer. If the survey holds no value to any other prospective buyer, I am not sure that I would invest that amount of money without a stronger written commitment and/or money from the prosective buyer. Skin in the game, that does determine how serious someone is about a property purchase.
I would talk with your attorney on the estate and a really good Realtor concerning these issues and how they are handled in your area. Ultimately your goal is to sell the property but is taking that much of a cost actually going to hurt you in the end.