marshalls of bury st edmunds is nearish to cambridge, they are apparently a nissan performance specialist, they are on our forums recommended garage list.
you might find something there, but i don't know how competitivly priced they will be. i've tended to find that nissan are over priced on their own 2nd hand cars.
get on to auto trader and piston heads, if your open to travelling you can have more choice and better prices.
i'm based in ipswich, am happy to take you out for a drive if you want to get a closer look before buying,
my car was from harrowgate, my car before that was stoke on trent. always makes for a good fun roadtrip