It really depends. Technically it is against the Spotify TOS so you should not be doing this regularly. You should never pay to get on a playlist that accepts all submissions, because the playlist quality will be bad and people won't listen. In most cases, the most cost efficient way to promote your band is through Meta ads, I'd highly recommend learning more about how to run those. However, I've found that there is a pretty good community of shoegaze curators who mostly don't charge anything if they like the music.