Cloudflare's enterprise pricing is, irritatingly, of the "contact us" variety (FYI typically starts around $5k, last I checked, and at least for us they weren't interested in reducing that by cutting all the shit we didn't need, such that they were effectively really expensive on a per-TB basis) but, to be fair, if you're doing any kind of real volume you're going to want to contact sales at those other places, too. Odds are sticker price is just an anchor for negotiations anyway.

[EDIT] However, you're right that the lack of even limited pricing transparency makes relying on CloudFlare at lower levels risky because it's hard to know what kind of expenses you might, later, be exposed to.