Your budget's only too low if you don't mind waiting for a while and looking round.
Many Defenders at, or under the 3k mark are fairly ratted or rotten (look out for serious rust in the outriggers, the rear cross member or the bulkhead. Of these, the bulkhead is fairly critical and is the most timeconsuming (and expensive) to change.
Expect to get a non-Tdi engine, unless you're lucky.
Vans are harder to obtain than station wagons.
Surprisingly, Range Rovers and Discoverys offer better value of money than Defenders (they were victims of higher rates of depreciation).
Having said that - some really good examples can be found and had for that kinda money - it really is just a case of being a bit carefull, thats all.
As for where to look - the words 'world' and 'oyster' could probably be applied!
Good luck with the search!
cheers
8)
Eeyore