Whats the budget? Will you work on it yourself? Are you keeping it road legal? What sort of Off roading are you hoping to do(laning/trialling/pay and play)?

SJ's are getting hard to find if you want a tidy one, for the cost of one with a few mods you can get an early Jimny. Same applies to Vitaras old ones are usually really rough.
Daihatsu sportraks are cracking but again hard to come by cheap.

Discoveries and old Rangies can be had for £500 but will obviously cost more than an SJ to run.