That's strange, he said his is from the 2003 year, I dont know much about Kona but after seeing a few of them in the thin tubing steel frames, it caught my eye and fancy one for myself.
It's definitely a nice frame, with the advantage of butted stays as well as double-butted main tubes - i.e., it was one up on the Cinder Cone that had plain-gauge stays. Made of generic 4130 though, so not quite as valuable as a Kilauea which was made of Reynolds 631 that year.
I wouldn't pay £150 - I'm not sure those black P2s (assuming you even want them) are triple-butted, and if not they're only worth c£15 (they're quite heavy and nothing like as good as the tb ones). I reckon the frame itself is worth in the region of £100, depending on precise condition.
A 97 Kilauea frame sold for £85 on eBay last week, and that included a Pace RC36, LX cranks, an unspecified bottom bracket and some not very good wheels. OK, that seems too cheap (bloody missed it!), but I reckon that package was worth more than a 98 Caldera plus P2s.