i had a great time in 2005. was on my own, but that caused no probs. camped and hostelled - 60/40ish. dunno how much i spent, as i wasn't that concerned, but it wasn't a huge amount.
i just did the south island, as i'm more into scenery than culture.
i did christchurch down to dunedin, across to QT and wanaka, across haast pass, up west coast, abel tasma etc, back down a bit to do arthurs pass and back to christchurch.
roads were lovely to ride on, no real traffic issues iirc. had 3 wet days in 5 weeks...
3 days sea kayaking in abel tasman was great, as was a scenic flight over lake takapo (i think) there i was allowed to take controls of the plane
i'd avoid the canterbury plains - boring as hell.
going from QT to wanaka you get to a pass after a steep climb, with a sign signalling a 40km downhill. bliss. ok, it was more rolling further down, but it was cracking...