Briggs has a lot of pull start assembly's on the market, maybe one of them would fit? Sorry about the starter, but a thought, if you have a starter repair place around you they may have something that would fit? Worth a shot anyways. 
What is the frame serial number on the generator? It will be in the format of EXXX-1234567. With that, I can look it up in the Honda parts catalog and see what's what. $600 does sound steep.I have an old Honda EM5000A generator that the starter has been removed from. In my attempts to find a new starter, I found that it is obsolete
I did check and the starter as a whole unit is no longer available from Honda. That specific starter was unique to that model generator, and our catalog does not show it being used in any other models.I have an old Honda EM5000A generator that the starter has been removed from.