What DID the Ferengi purchase warp travel with?

I want to believe Latinum, but that depends on if Latinum was at the time valuable with other species as well.

Sometimes I theorize that the grand Warp purchase was just a conspiracy, and that Ferengi scientists made it on their own-BUT-the Nagus at the time covered it up as the greatest purchase of all time, to inspire Ferengi culture and embolden their entrepeneureal spirit.

Because for real, can you imagine how INSANE the concept of being able to BUY warp travel is? If that wouldn't put faith in the value of Latinum I don't know WHAT will!

BUT-once again, it all depends on if Latinum was rare/valuable before Ferengi started using it as currency.