I concur, if money really is an issue then farmer's walks/carries and timed hangs can be great grip strength/endurance exercises.
You could also try:
Timed Barbell holds- load up a barbell in a rack or up on blocks (you want to be able to grab the bar and then just have to stand up a couple inches to be at full "lockout" in a deadlift position. You want to use enough weight for the exercise to be challenging, but not so much that it is ripping the weight out of your hands by the end of the set (or else your posture will likely suffer and you may strain the tendons in your hands). I'd start with something like 30 seconds per hold and then work up till you can hold that weight comfortably for 60 seconds. At that point add enough weight to again make it challenging to hold for 30 seconds.
Towel pull-ups- this can be done by either simply wrapping a towel around the pull-up bar to thicken it, or by draping 2 towels over a bar and grabbing one in each hand and simply doing pull-ups
Thick hand shrugs- place 2 barbells in a power rack and load up one side with however much weight you want to use for your shrugs and the other side with enough weight to keep the bars from sliding around too easily (conversely you could also place the ends of the bars against the base of a wall ala old school t-bar rows). Now walk around to the outside of the rack and stand between the ends of the barbells. Grab the bars on their ends (which will be thicker than the bar inside the collars), pick them up and do your shrugs. You could also perform your times holds like this as well.
One additional piece of advice is to do some finger extension work if you are going to do a lot of grip work as this helps keep the hands healthy and stave off muscular imbalances (which often lead to overuse injuries like carpal tunnel or Tendonitis). All you need are a few medium strength rubber bands to do this. Place them around the outside of your fingers (tips of your fingers all touching) and then try to open your fingers as wide as you can against the bands. Add more bands if you need more resistance. You can either do reps like this or static "holds".
Hope this helps.