Buckner got $135,000. As BurgherKing noted in the minors recap thread, that amount is surprisingly low, as was the $190,000 for Roth.
Pirates Prospects has a rundown of some of the remaining possibilities. There are two remaining early rounders, SS Adam Frazier (6th) and RHP Buddy Borden (7th). P2 notes that Frazier is likely to sign, but Borders has been seeking above slot money. He strikes me as having been drafted about where his talent warranted, so maybe he won't get it.
P2 calculates that the Pirates have $107,800 in above-slot money left, plus another $435,345 that they can spend without losing a draft pick if they don't mind paying a 75% tax.
UPDATE: The Orioles acquired RHP Scott Feldman from the Cubs in a four-player deal that also saw the O's send some international bonus pool money to Chicago. Int'l pool money could be a bargaining chip for the Pirates, who haven't been linked to any of the top international prospects who became eligible to be signed today.