Walk right up and take your pick of the free agent running backs. There are a lot out there and the price tag will be much lower than expected.
The top tier of free agent running backs is pretty much set, with Buccaneers RB Doug Martin, Dolphins RB Lamar Miller, Bears RB Matt Forte, and Jets RB Chris Ivory. Miller, the youngest of the four, is expected to see contracts valued between $4-5 million per year. That's a complete bargain and it really sets the market.
Outside of those four, there is Texans RB Arian Foster, Cardinals RB Chris Johnson, 49ers RB Reggie Bush, Washington RB Alfred Morris, Jets RB Bilal Powell, Lions RB Joique Bell, Packers RB James Starks, Saints RB Tim Hightower, Saints RB Khiry Robinson, and the Patriots own RB LeGarrette Blount. These players have flaws, whether it's injury (Foster, Johnson, Bush), lack of dynamism (Bell, Starks, Hightower, Robinson), or are one trick ponies (Morris, Powell, Blount), but they could all be boom-bust options in the Patriots committee.
Additionally both Eagles running backs DeMarco Murray and Ryan Mathews are available at the right price. Murray's contract is a gross $8 million per season and is out of the question, but Matthews would essentially be under a 2-year, $7 million contract.
That's not to mention that the Broncos placed the original-round tender of running back C.J. Anderson. Anderson was an undrafted free agent, which means that any opposing team vying for his services wouldn't have to give Denver a draft pick in exchange. NESN's Doug Kyed laid out a pretty great justification for going in on Anderson this free agency period, and Anderson himself has nothing but great things to say about Patriots quarterback Tom Brady.
All of this depth at the position will likely drive the price down of these middle class players on the open market, which plays very well into the Patriots needs and salary cap management. Every single one of those players listed would be a better option than Joey Iosefa or Steven Jackson.
While Blount will likely be available for the cheapest option, players of greater talent could fall within the Patriots comfort zone of contract offers.