My top picks:

KLR 650: The claw hammer of motorcycles. Reliable and durable. Not necessary the best tool for any job, but an adequate tool for many jobs. Huge aftermarket support for mods. Heavy. 87-07 no significant changes. 08-current got better fork and brakes.

DRZ400: More dirtworthy than most other options, at the expense fo highway comfort and extreme long range riding. Lighter than a KLR. Vastly better suspension.

DR650S: Air cooled Suzuki version of the KLR, with somewhat better dirt capability. Once again, huge aftermarket support.

XR650L: Honda's answer to the KLR. Lighter, slightly better suspension and brakes. It's an air cooled XR, so it's as reliable as an anvil. Worldwide, it probably has the best support network of any brand or model.

You should be able to find any of these in your price range if you look around. PM me if you have any specific questions about a given bike.