@is2017overyet Dan John has said some interesting things about getting the most out of the kettlebell you have.
You can substitute knowledge for equipment and get very far.
The first question to ask is how many reps can you do of key exercises with the kettlebell right now?
Unless you have experience or you are already a monster, there is almost certainly a range of things you cannot yet do with 20kg.
Start with the two handed deadlift. That’s easy, start with two handed swings. That’s easy, one handed swings. Learn to goblet squat. That’s easy, learn lift to rack position with two hands. That’s easy, learn to clean with one hand. That’s easy, learn to press. And add in squats with the KB in rack position (over time, build your repertoire of KB squats). Once you can press it 5 times you can move into Neupert’s DFW (free. See the FAQ). From here progressing to the Giant is a good option. Depending on your starting point, you might have spent a bunch of time getting this far. Or not. All depends.
Dan John’s Armor Building Complex (ABC) becomes an option, too. Be sure to look it up and heed Dan John’s advice on single KB ABC (free on YouTube), and his advice on training frequency (do it no more than three times in two weeks, so two times one week, one time the next week and so on).
At this point you could build towards being able to do the secret service snatch test. Mark Wildman has great material on building time under tension programming (also free on YouTube). And he has a program he explains building towards this test.
If you get to where you have accomplished all of this and you still cannot yet afford another kettlebell, fear not. There is still more you can do.
For example, you can learn to hold the bell with the handle gripped in your hand and the ball up above your hand and you can repeat a bunch of stuff this way. Holding the bell this way is no joke.
You can also do a bunch of carrying the KB. Start with suitcase carry (single arm farmer carry). You can simply increase distance down the street to make it more challenging. Not challenging enough, switch to carrying the KB in front of your chest with two hands (like goblet squat). And then in the rack position. And then held like a waiter carrying a tray. And then as described above with the ball above your hand. Once you have mastered these, you can hold the bell overhead (be sure you can do this safely before you attempt—dropping 20KG on your head is not good). All of these can have distance, going up and down hills, going up and down stairs etc added for more challenge.
Learn Turkish Getup with nothing. Then a shoe (or whatever). Then a water bottle. Build your way us with what you have (gallon jug of water is just under 4 KG, then sub in barbells or something that you can handle till you get to 20 KG).
Make a sandbag (plenty of videos on doing this cheaply. Carry them around. Learn some sandbag exercises on YouTube.
Carry stuff in a backpack (rucking).
Make a pull-up bar with a length of pipe. Home Depot and the like will generally cut it to the length you want free when you buy the pipe. Not very expensive and a pull-up bar is super useful.
Learn calisthenics.
You can become a monster with whatever set of these ideas appeal to you.
