I have just damaged shifter and it is no longer usable. Is it possible to replace it with something cheaper and more available? It is just commuter/winter-bike, so I just need it to work and less it costs, better it is.
Go to your local bike shop and ask for something used out of their parts bin. They’ll often have shifters left over when someone upgraded. My bike shop would throw in the part for free if I paid for labor, but in either case the cost would be trivial. It’d be worth it to get the derailleur cable (both inners and others) replaced at the same time.
Reading Sheldon’s page on Sachs/SRAM IGH it appears that the cable pull for that particular seven speed internal gear hub may not be standard. It may be better to just replace like with like. Again, your local bike shop may have the spare part in their parts bin. A local maker space may be also able to fabricate the part out of nylon or abs using their 3d printer.
If you just need it to work, a friction shifter will work with just about anything. Your bike shop should be able to give you one for free or close to free.
The cheapest option is drilling in grip and putting there some metal replacement for broken part. For half of the price you can get S5 shifter - broken part may be iterchangeable. Last, but probably the best option is to search for used parts. You didn't confirmed, but I still assume you're in Poland. Have look at this bunch of offers: