If you don't have money to buy a lot of storage media, stop acquiring new files and ration what storage space you already have. If you don't create any new files, you won't have to buy new media. It's a logical decision, if somewhat restrictive.
If you carefully conserve existing storage space, you can keep your current data until you no longer need some files and delete them to make way for new information.
You should save at least two (preferably three) copies of all important files to two (or three) different types of media.
Do not keep all your files on one hard disk, SSD, portable drive, USB memory stick, optical disc, etc. That way, if one drive dies or you suffer a ransomware attack, you'll still have another copy on different media. Spread the risk around.
I bought a bunch of old 3TB 3.5in server hard disks recently for $12 each. Even if some of them die tomorrow, I can afford to back up files to multiple drives for very little expense.
I also save data to second-hand 800GB LTO4 tapes costing $2 each. A full height tape drive was only $33 and the SAS controller card another $15. I purchased enough tapes to last me some time and if a few of them stop working, I have multiple backups on other media.
If you describe your storage needs in terms of Terabytes, we might be able to offer suggestions.