Let's get to the links...
Marcus Mariota remains the only unsigned No. 1-pick; OMG can Chip still get him?!? - PhillyVoice
According to Lynch (via overthecap.com), before the Eagles started signing their own rookies, they had a cap for drafted rookies of $4,570,941. That cap money cannot be traded, but it could have been divided among drafted players any way the team wanted. So in other words, if say, the Eagles traded for Mariota after the draft, they would have had $4,570,941 to pay seven draft picks instead of six, including Mariota.