OAKLAND, CA - NOVEMBER 03: Center Stefan Wisniewski #61 of the Oakland Raiders snaps the ball and blocks against the Philadelphia Eagles in the third quarter on November 3, 2013 at O.co Coliseum in Oakland, California. The Eagles won 49-20. (Photo by Brian Bahr/Getty Images) Stefan Wisniewski, center. (Getty Images)

By Dan Durkin–

(CBS) After more than a half-billion in guaranteed money was spent during the past week of NFL free agency, the market has hit a lull. The majority of “big name” players have already found new homes. However, there are still players available on the market at positions the Bears have needs at that may pique general manager Ryan Pace’s interest.

Pace stated his goal was to use free agency to fill needs on the roster to ultimately open up the draft board to select the best player available. Signing outside linebacker Pernell McPhee, safety Antrel Rolle and wide receiver Eddie Royal did address some of the Bears’ most-glaring needs, but this roster is still riddled with holes.

Currently, the Bears have 56 players under contract, which is the lowest total league-wide. They have just a little over $15 million in free cap space, which is more than enough room to make some value signings.

Let’s take a look at some of the names left on the market who fit what the Bears still need.

Inside linebacker Mason Foster

As it stands, the Bears don’t have enough competition at the Mike linebacker spot in their new 3-4 defense and need a more reliable run player to fill that role in Vic Fangio’s scheme. Entering his fifth NFL season, the 26-year old Foster already has 54 NFL starts and has averaged 86 tackles per season.

Lovie Smith brought his Tampa-2 principles with him to Tampa Bay last season, which requires the Mike linebacker to carry receivers up the vertical seam, a role for which Foster was miscast. Foster has scheme versatility but would be best suited inside in a 3-4, where he can utilize his read-and-react skills to aggressively attack the run downhill.

Center Stefen Wisniewski

Despite having Roberto Garza signed up for his 15th NFL season, the Bears need to address the center position both in the short- and long-term. Recall if you will, Garza was signed to a one-year extension by former general manager Phil Emery, a move that Pace may not have made if given the option.

Wisniewski has been a durable and productive starter for the Raiders, making 61 starts over the past four seasons. The soon-to-be 26-year-old originally started at left guard but made the transition to center in the 2012 season. While he can be over-aggressive in his pass blocking sets, Wisniewski is a reliable run blocker who would immediately challenge Garza for the starting role and provide the Bears with a building block for the future.

Defensive lineman Randy Starks

When Pace and John Fox were asked about which players on the current roster project as defensive ends in their new 3-4 scheme, there was a long pause before Fox provided a vague answer. The signing of Rolle proves that the Bears are open to signing reliable veterans to help lead their turnaround on defense, and the 31-year-old Starks still has a lot of productive football left.

Starks truly transcends scheme. He’s been selected to the Pro Bowl both as a base 3-4 defensive end and a 4-3 defensive tackle. He’s a powerful player who wins with leverage and length at the point of attack. Starks has been a durable player, missing only five starts over the past six seasons. He would immediately rise to the top of the Bears’ depth chart at the four-/five-technique defensive end position.

Cornerback Tramon Williams

Editor’s note: Williams signed a three-year contract with the Cleveland Browns hours after this column posted.

If the season started today, Demontre Hurst would again line up as the Bears’ starting nickel cornerback. As last season demonstrated, this was a role Hurst clearly wasn’t prepared for as he struggled in pass coverage from the slot. The 32-year-old Williams has been a productive starter for Green Bay, logging 28 interceptions over the last eight seasons.

Williams has played under Dom Capers, whose scheme is similar to Fangio’s. In fact, Fangio was Capers’ defensive coordinator in both Carolina and Houston. Their schemes require corners to aggressively play press on the outside, which allows for mixed coverages up the middle and frees up blitzers from the second and third level.

Dan Durkin covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter at @djdurkin.