My secret to grip strength on a budget is to do things that the only weight it requires is your own. I did thick bar pull-ups by wrapping my bath towel around the bar, built up my fingers from doing gorilla exercises and fingertip push-ups to the point where I can do them explosively off the ground, hook my fat gripz to a bar and have at it yet still made progress with my grip strength. Not everyone has the ability to get expensive stuff to make themselves better and even if they could, don't take it for granted. I believe in the art of using your brain and using your money for things that matter most to you. Here's a list of what you can use for under a few bucks....
Left over tires for Hammer striking
Your towels to build pulling power
Removable Doorway Pull-up Bar
Step Stool for elevated Push-ups
Buckets to fill water and carry
Many ways to build grip power without needing to spend a ton of money, one of the greatest arm wrestlers of the 20th century Mac Batchelor used bottle caps between his fingers and other things that made his grip so powerful, no one was able to beat him. Use your imagination, be willing to do what you can without needing a whole lot for very little. Use your brain, not always your wallet.