First looks like an Echinocactus grusonii.

I got hooked on a guelzowiana once and never again - I tried to push into it with my finger, but then I tried to pull it back and I got hooked by atleast 4 hooks. Then I tried to free myself with a finger from my other hand, but I got stuck with that finger, too. Too afraid and unable to do anything...

Used to be green but it went dark and got brown spots. Edit: Huernia

3. Looks like a small Mammilaria haageana

Looks like a Huernia. I can't tell the exact species without seeing the flower, though.

Don't think I'll be getting root rot anytime soon, thanks.

So I bought a few new cacti, I cleaned the roots of the old substrate and left them to dry a few days. Potted them in my substrate and now I watered them by a mistake instead of keeping them dry. Should I take them out and dry roots again or just let them be?

Since you're looking for cheap stuff and said pumice isn't availible, think of a mineral material that will increase drainage and isn't organic.

Some people use large tweezers, hold the cactus up and problem solved. No damage to the cactus, no damage to the hands

Yeah I have a HUGE opuntia right there outside. I was just wondering about other kinds of cacti, I'm probably going to cover them at winter to keep them warm and dry

Most basalt is also on the alkaline side, making this soil mix good for nothern cacti, but not for southern cacti. You can still use it on both, but if you want to get serious, you can add more organic components and less basaltic gravel and biochar, as long as the drainage is still good.

It's a good idea to reduce basaltic gravel use in the mix, but that also decreases much needed drainage. Now you've got 40% of gravel, 40% top soil and 20% biochar? This is just fine for some kinds of cacti, but no mix should be uniqe. You need to adapt to the cacti you have. I recommend a mix of 1/...

Yes, I've noticed that it's very light. I was surprised by it. My mother always said it has the properties of styrofoam...
Thanks for all the help!

Yeah that's why I was asking. Where I am there's a shop that sells perlite, but I'd have to get pumice through sites like e-bay and pay a lot for shipping. Thanks for the answers

But is there any difference in cactus growth (or general plant growth) if perlite floats to top? Is the drainage still good or would root rot and similiar problems occur? Also, wouldn't it float back down as time goes?