I disagree with the OP.
Hartlines opening negotiating position is unlikely to be what he signs for regardless of where. I say let's negotiate with him and try to sign him to a deal the team can afford. He was our best WR and is a legitimate #2 WR, which we need. Bring in Jennings. If we can't fit both of them under our cap then we mismanaged something somewhere besides WR.
Rookies have affordable cap numbers. Yes we can draft a couple WR's and sin both Hartline and Jennings. Non-rookie veteran minimums aren't the savings you might think, and the coaching staff will not be satisfied with a mediocre journeyman or an UDFA. I'll go on record now as predicting we will draft 2 or 3 rookie WR's. That's a position which is vital and at which we are talent-starved.
This offense needs 4 good WR's. We routinely start 3, a split end (currently missing entirely from the roster), a Flanker (where our best WR Hartline plays), and slot (where Jennings and Bess both primarily play).
Realistically, Bess can ONLY play the slot. Jennings can move around and play all three well, but is at his best using his quickness in the slot. Hartline can be moved around as well, but is most useful working the sidelines rather than the slot. To keep WR's fresh and send one deep very often, you need 4 WR's for those 3 positions.
Jennings, Hartline, with Bess and Matthews adding depth for injuries still leaves one starting split end position open. That is our deep threat starting rookie WR.