Any method to pay for Amazon stuff, while not owning any credit card?

You can trade TF2 keys or something for it with someone else.

Buy a prepaid visa?

buy a $10 prepaid credit card from retail store/gas station/walmart ect?

Paysafe

Try Swagbucks or one of those types of places. For 1000 swagbucks, you could get 2 $5 Amazon gift cards sent to you the next day. It isn't hard to reach 1000 swagbucks when you are new, since you haven't done any of the offers, yet.

I should add that I have $7,50, but amazon doesn;t accept Paypal (which I used for any online purchases)

Can you buy an amazon gift card around in a store around you?
Trading is rather popular. Im sure you could find someone to take that 7.5 paypal along with something else you might have.

Since it's a sale and time matters, go to a grocery store and either buy an Amazon gift card or a Pre-paid credit/debit card with cash. The Amazon card doesn't cost anything extra, but it has to be used on Amazon. The prepaid credit card can be used anywhere, but there is usually an extra fee.