Aside from all of the equipment being offered, what about his customer base? I did not see you mention that in there? I agree with Magic Dave if its only equipment. I would negotiate with him I would settled for something closer to 10k. After all you have given him 5 years a good loyal service and quality work. Ask him to put in his customer base and phone number transfer. He is retiring and any phone calls he received he could simply pass them onto you. Just a thought though, you can always start out on your own as well. But it will take a while for you build up a customer base.
Hope this helps, and good luck in whichever decision you decide to make.