I third the notion that a fee to sea trial will be a nonstarter for a sizable buyer population. If I was presented with those terms, interest would stop there.
I would not pay to get your own survey, unless you are using it to actually make pre-sale repairs. Just let the buyer pay for their own survey - many will insist on it anyway and once they commit that $1-2k or more on the survey they have an small additional incentive to close the deal. If you are worried about being blindsided with findings at survey, so what? The prospective buyer will use them to offer a reduced price or negotiate repairs, and you will get the information for free and can proceed accordingly - reject and end sale, adjust ask for next buyer, continue on with deal etc.