We started out as slid.es and then bought slides.com. I won’t share the exact amount, but I believe it was 5x our yearly revenue at the time so safe to say it was a big investment. We haven’t raised any money so my co-founder and I had to pay out of pocket.
(iirc) It was originally slid.es and the slides.com domain was added later, I know it's not an answer to your exact question, but slid.es was a pretty good start point too :-)
(It became a defacto go-to tool for slide decks for me because it was so memorable)