I've recently re-installed windows from scratch.
It comes with a demo of a paid antivirus, but I'm not looking forward paying that much for an antivirus.

I could get Avast again, although lately I was a bit tired of its frequent notifications.
So I thought I should ask: Any recomendation for (free or cheap) antivirus?

I think a long time ago I used Avast for a free demo and I have used whatever the main 'free' one for Macbooks is but mostly I've just not had an antivirus? Seems to work fine for me.

You are definetely bold. Much bolder than me.
I would not keep my computer without an antivirus, just in case.
Specially not since I use it to log into my bank account or my paypal account.

I would say using just windows defender is good enough, and it updates along with your windows updates (and is free) - I would go against Avast:

"Avast Antivirus and AVG AntiVirus Free version were collecting user data, which was being resold to personalize advertising through a subsidiary"

Window Defender on its own?
I had always thought it needed an aditional antivirus!
Learning something new already.

I'm afraid I mostly rely on frequent backups so that if I get a virus I can just wipe the hard-drive and reinstall everything, and start over from factory reset.

It's drastic, but I don't have a lot stored on my computer, so it works, and it means I don't have to fuss with anti-virus stuff.

To be honest, the one year I was trying anti-virus software, I found that it made a mess of my computer worse than most viruses. Bogged everything down right awful!

Seconding PastelWitch, I also just rely on windows defender at this point. Back in the day, I used Avast but it would always have issues updating itself. Then my mom bought McAfee and that worked, but I ALWAYS had issues with it slowing my computer down to a crawl.

AVG wasn't bad, but if you play games on your computer you will need to disable it before running game updates or patches.

Also putting in a vote for Windows Defender. I struggled for a long time with Avast slowing my computer to a crawl, so I was looking up what kind of anti-virus computer savvy people tend to use, and the overwhelming answer seemed to be "just use Windows Defender". As long as you're not downloading suspicious files, it tends to do the job just fine without any extra help.

Wow.
This is really surprising me.
I mean, I thought that was only good for kiddos who really don't manage any risky data - bank accounts, credit cards, etc.
I should research more into this Windows Defender...

...Good to know. Learn something new every day.