If it's orange, are you sure it isn't a 97 frame such as this?
http://www.konaretro.com/articles/catal ... Page19.jpg
If it is, then although it was the lowest-priced aluminium frame in the 97 Kona range, it was actually a double-butted frame that I believe was identical to the Muni Mula, but sold with cheaper components and a P2 fork. As such, I think it had a bit of a reputation as very much a hard nut's bike.
Personally, I would suggest that a Bomber Z1 is far too long for a frame sold with P2s, but AndrewL would completely disagree with me (see certain other threads).
I would agree that as a frame it is worth less than a Lava Dome, so maybe only Â£50-60. But if it's a 97, they are very nice-looking bikes and if you could pick up a good condition double-butted Kona in orange for Â£50, that would be pretty good value.