Quaife reversing box

Hello all,

I'm part of a team building a bike-engined Reliant Kitten but on a very tight budget, is it possible to pick up a Quaife reversing box second-hand and if so can anyone give me an idea of price?

I know they're around £700 new but that's literally 7/10ths of our budget so it's a definite no-go :)

Thanks in advance,

Matt