look on milweb or the classifieds of classic military vehicle mag, i'm sure i've seen mj's for the £3-4k region. like you i was looking for an mj last year but decided to opt for the daf instead, it's not as simple or bomb proof but it is much nicer to drive over any kind of distance. trust me when you hit 50 in a bedford the steering wheel will shake violently which can be quite exciting down hill with a trailer.
i bought 2 daf's for £1850 each from withams tender and both were in good shape.
if you want bomb proof go bedford if it's driveability go daf.
good luck with the search i'm sure you'll be happy either way as both trucks are good it's only a matter of how much money you part with.
rick