Buy a cheap eBay 2.5L replacement for $2500 and swap it yourself. With new plugs, air filter, oil, oil filter, and coolant, you'll be back on the road for less than $3K.
Here is one with 76K miles asking $2675 + $250 shipping. I'd ignore the BIN button and send the seller a PM and offer $2500 incl shipping.
https://www.ebay.com/itm/1999-Porsche-Boxster-2-5L-Engine-76-189-miles/192506591508?fits=Model%3ABoxster&hash=item2cd2497914:g:zsAAAOSwOxNay6vr:rk:10
f:0
Sorry, just saw that you're in Hawaii. You'll have to get a quote for shipping. Still worth pursuing.