I believe that is about average on Japanese bayonets nowadays.
I've seen them here for less.
Offer him $80, and get him down to $100 - or if you can't
live without it, pay the asking price...............!
I don't know a thing about bayonets or pricing but have been keeping my eye on a number of these Type 30's on Ebay. Prices range from $40 - $100 US it looks to me. I'm guessing the Type 30 is very common.
With bayonets (and indeed most things people collect) it comes down to rarity of the particular item and its condition-the bayo is a Kokura arsenal type not very rare and the condition is average or so-would try for a better example for the asking money, imo.