Ok; Here is a low-cost backup plan. This is going to be very detailed.
First; Backup Basics: Every file on your computer has a "modified" flag. Whenever the file is changed or created, the flag is set. Backup programs are usually the only programs that un-set this flag.
There are 3 types of backup
FULL: Backup all files. The modified flag will be reset when the file is backed up.
DIFFERENTIAL: Backup files with the "modified" flag set. The flag is NOT reset
INCREMENTAL: Backup files with the "modified" flag set. The flag IS reset after backup.
There is a 4th type (not much used) called "LIVE BACKUP" where the backup program runs in the background and backs up all files immediately upon change. I did do that when I was working, but not now.
This is my preferred backup method. Setup your software to do FULL when requested, and DIFFERENTIAL other times. I make a FULL, then 12 DIFFERENTIAL, Switch backup media and repeat. If you need to restore the data, You restore using the most recent FULL backup and then use the most recent DIFFERENTIAL backup. Done. INCREMENTAL requires ALL the INCREMENTAL backups to be available to do a full restore.
I run my backup program every 2 weeks. It is on my schedule. Your comfort level may vary.
OK; How much storage? Look at the "Properties", "Used Space" of your hard disk(s)how much storage do you have? Multiply by 4. This is the size you need for backup media.
When doing backups the equation is Money = Speed! The more you spend the quicker your backups will run.
Use USB sticks. They are relatively cheap, easily transportable, and perfect for this task.
Go to Amazon and purchase several USB drives. You can get 10 of these USB drives for under $100. Get Sandisk USB drives and DO NOT BUY THEM FROM EBAY!!!!! The ones on Ebay are likely FAKES! They will appear to work until you need to restore them and then you will get data errors.
Another option is to use a USB connected External Hard Drive. These are available in 2-14terabyte drives sizes. Cost $70 - $270
SanDisk 128GB Flash Ultra (10 Pack Bundle) 3.0 USB Flash Drive
SanDisk 512GB Ultra USB 3.0 Flash Drive
Search Amazon for "western digital USB external hard drive"
Note: Lately, USB-C connectors are becoming more popular. Be sure to check this detail.
OFF-SITE storage: Give a copy of your backup to a friend you trust and let him keep a copy outside of your home. I have a fireproof & water-proof safe. Me and a friend exchange backups when we see each other. (Yep, I'm Paranoid!) Search for "South Korea Data Center Fire"!
SOFTWARE:
There are many free or under $100 backup solutions. Be sure to test the restore function to verify it works. Be careful with the FREE options some of these DO NOT include the restore function. Easeus ToDoBackUp (paid) is a good one. Nero also has one I have used.
Run your backups over night. Start the backup before you go to bed. Some backup programs have a "Shutdown Computer after backup complete" option.
DO NOT save your backups to the cloud. It is easy and (corps / govt) willing to (pay / bribe / threaten) can get access to it.
RANT MODE ON: Do not go for any subscription. If the company goes under or abandons the software you are sh__t out of luck!
WHEEEO that is a long one! sorry for the length, I was trying to make it as free from techo-babble as I could and explain the details and why you do them.