PSA: I've seen scams for land sales like this before. Check the land is allowed to be built on, and do your homework first.
(Phoenix1969: Not saying you're a scammer, just want people to know what they're getting into.)
I live within a dozen miles of that spot. Not only can you build there, but you can pretty much ignore all regulations. Probably half the houses there have no permit.
As for price, seems reasonable. Decent lots in the Puna area start around $5000.
Lots around PahoaCool what part are you located in? i'm on east side.