Since you are new to the hobby, you don't need a locker, all a locker will do for you now is get you into trouble on the trail. Yes a locker is a plus to have on any trail but not necessarily needed when starting out. My buddies and I all wheeled for years before getting lockers, we had to do a lot of digging and recovery work, but we also learned a lot more.

The first thing you need to spend your money on is recovery gear(quality tow/snatch strap, shovel, hi-lift jack, tire plug kit, duck tape, large zip ties, gloves, 2 ton come-a-long, a set of hand tools, etc.) a first aid kit, an on board air system(compressor plumbed to a tank, a CO2 tank, or a couple of 5 gal air tanks) to refill your tires after airing down for better traction/ride on the trail, a way to carry it all securely in your truck, a CB, and recovery points at the front and rear of the truck. You should have one factory tow hook on the passenger side, you should add another one to the drivers side. You will also need a way to be towed from the rear, if you have a drop hitch reciever they have recovery hooks designed for them, or you can make your own. If you only have a standard rear bumper, you should buy a drop hitch reciever, or a rear bumper with teh drop hitch reciever built in it. After this you need to invest in rock sliders to potect the rocker panels(the area below the doors), the sliders alos give you a place to lift the truck from if you need to reseat a bead, lchange a flat tire, help get you unhi-centered, and get a good solid front bumper. These will help to keep your truck's sheet metal looking clean, and allow you some room for error when out on the trail.

The next thing you need to do is find a buddy with a 4x(never go with one rig), or join a club, and hit the trail. Once you have an idea of what you want to do on the trail, then look into things like lockers and winches. There is a pretty long learning curve to this hobby, wheeling an open diff'd rig is IMO the best way to learn how to read a trail and pick the right line much better, you learn how to correctly spot another vehicle and how to be spotted, as well as what helps to get a vehicle unstuck and through a difficult section on the trail, all of which is needed even with lockers, dual t-cases, large tires, etc. You want your vehicles ability to always be behind your driving ability, you should only modify your rig as your driving skills advance.