Pentax Spotmatic would be my first option, if you don't need to switch lenses very fast or find using a microprism spot annoying. The M42 lenses for the Spotmatics are very good. The off-brand lenses for M42 are mostly cheap and cheerful. If you want to stay with Nikon, I think the EM, FG or FG20 might be good options for suicide missions in unknown territory. The various off-brand K mount cameras could be another option, as would a Pentax K1000 (same specs as the Spotmatic but with a K mount).