BridgeDB's email whitelist should include @riseup.net
Yahoo accounts go for $0.005 USD apiece, and Google accounts go for $0.10 USD apiece. I tried to buy a Riseup! account today, to see how much it costs, and failed. Then I tried to buy invite codes to make an account. I couldn't do that either, though I did find two sketchoids on sinister.ly (a "closed forum") who were offering Riseup! invites for "50 SP". I then tried find out what currency "SP" was, only to realise that it is some point system on sinister.ly.
When I pointed out that forum posting to the birds in irc.indymedia.org#riseup, they quickly banned the user. They also said they would be glad to have @riseup.net accounts supported by BridgeDB.
In short, I can't give you a price in USD, so I don't have a proof. But I can say that I was not able to get a Riseup! account on the black market, ergo doing so must be some non-trivial task.
I propose we whitelist @riseup.net. Dissenters, anyone?