Shipping that boat from San Diego to Hono or Hilo will run right about 3.5 to 4K. And good luck finding one in CA...
Try to work the guy a bit, but like you said - boats in HI are worth their weight in gold, especially running. That's only the third Seacraft I've seen listed on the islands in the past year...the last i saw was a 30 y.o. seafari 20 for 11K
Price is probably high by mainland standards but you guys live better...
If you have the money, go for it -- maintain it, and if you have to sell it, you'll almost certainly get your money back on the sale. Not many boaters can say that.