From what you describe, $5000 is still pretty high. Especially, without the main blocks, which set you back $400 -$500. Again, it is hard to say definitely without seeing the boat, and then what is your local market like.
a custom 140 racing jib (he says alone worth over a thousand)
Question is -- what is this racing jib worth to you? H17S is not a racing class, I would guess, you would be happy with a stock jib (only guessing...)
If I was to sell it today I would aks about $5000.00, but it now has many refinements and additions (i.e., cat trax, a sail tube, new cross beams with integrated tracks, custom integrated jib track cars, heavy duty standing rigging, new to good sheets, two sets of sails in good condition (OME and a Whirlwind squaretop), extra rudder, extra centerboard, 8:1 downhaul, 7:1 mainsheet, well you get the idea).
This sounds much more what you are getting.
extremely friendly, knowledgable, and good guy and likely will sail with me after I purchase the boat.
If you are a beginner, there is a definite value in this. Get him go sailing before you buy!
I would go with $4000 -$4500.