Proton VPN has a free plan that is fine if you just want general privacy from your ISP. If you want to do more like torrenting or circumventing geoblocking, there are probably cheaper options although Proton VPN does have significant Black Friday sales (which I think you just missed, unfortunately).
That’s not true, I have been a customer for several years and regularly receive offers on my current plan during the big sales. The problem for me is that they lowered my VPN Plus monthly rate to $5 a while back and the promomotional offers usually reset to a rate higher than that, so even though I would save more in the short-term I am locking myself into a longer and potentially more expensive contract with them in the longer-term. I don’t know if this is bait from them or an oversight - I did notice that the most recent Black Friday promotion said it would reset to my discounted price at the end of the promotion so maybe they’ve changed it. I still didn’t take them up on it, though.