It seems you have the right approach - spend a little bit of money and see if you like it. Plus a budget like that will force you to get your fingers dirty and know how everything works - which comes in pretty useful when you break down on the trail which will happen.
One way to keep price down is to buy a vehicle they made millions of. Chevys are good, so are Jeep Cherokees, and Toyotas. Landcruisers, and the stereotypical Jeeps (CJs, YJs, and TJs) are popular but also more expensive.
Unless you're doing some gnarly wheeling, a winch or even a high-lift will get you out of most stucks. A high-lift costs less than 50 bucks used. So you can leave your diff's open and run crappy tires that you get second-hand.
Here's a list of things to buy:
1) Factory service manual - expensive ($100) but it will tell you *everything* about your truck
2) First aid kit
3) Fire extinguisher
4) High-lift, chain, and strap
5) 4" Lift kit
6) Bigger tires (33's or 35's)
Here are two good trucks:
Full size Blazer: (pre-76 if in California) These are big trucks with V-8s and reasonably strong axles. the tops come off which is cool and there are billions of parts out there and people that know how to work on them.
88 or 89 Jeep Cherokee: Again, millions of these made. Look for one with a Dana 44 rear end, a 4.0 motor, and a front axle that *does not* have a center axle disconnect.
There's a guy near me who regularly picks up 88 Cherokees for $500 (running) and throws big axles underneath (yep, chevy and ford stuff, HP Dana 44s, 14bFF and 9"), converts the front to leaf springs, and beats on em. The driveline seems to do OK (4.0 to an AX-15 to a NP231). He does do a SYE conversion.
Just some ideas. Most important is have fun. Get a rig, go play in the mud and run some trails. Find people who have done this before - they are usually very nice and like to talk about their rigs. Good stuff.
