A) What's the most he's willing to pay?
B) What's the least you're willing to work for?
If A<B, no deal. If A>B, somewhere between the two.
You know what B is, you just need to find A (without revealing B).
As far as real $numbers, I have no idea. Is there climbing involved, power lines,, nearby buildings, how tall? Too many factors. Getting a quote from a pro may be a good starting point (though that will ****-off the contractors here who rightfully resent their time being wasted).
But note: A pro is not just selling their services, their also selling / accepting liability. Are you? Is this part of your price?