Offensive line and linebacker are two obvious positions for the Buffalo Bills to target in free agency.

The Bills need to find a starting-caliber player at left guard, a problem spot all last season. They could use some help at offensive tackle, even if they aim to find one in the draft. There are looking for a veteran linebacker to help toughen up the middle of their defense.

“We’ll certainly be active in free agency,” Bills President Russ Brandon said last week.

That doesn’t necessarily mean the Bills will – or should – spend for one of the most expensive players on the market.

However, the Bills like to fill some of their needs in free agency in order to give themselves more flexibility in the draft. They also have enough money to fill holes, with more than $23 million in space available under the salary cap.

The NFL’s free agency season opens at 4 p.m. Tuesday. Teams were allowed to start talking contract specifics with player agents as of noon Saturday.

There will be a lot of capable veterans signed for good value after the first wave of top free agents sign this week. That’s when the Bills could stand to add depth at just about any other spot on the roster. Of particular interest will be whether the Bills sign a veteran backup quarterback and what they do at tight end.

Here’s a look at who the Bills might target at key positions of need:

Guard: The Bills tried to make left guard work on the cheap last season, but Colin Brown flopped and Doug Legursky wasn’t physical enough. If the Bills want to spend a lot of money, they could target Denver’s Zane Beadles, who made the Pro Bowl in 2012 but was inconsistent in 2013. He’s a talent.

Less expensive, but not exactly cheap, would be Kansas City’s Geoff Schwartz, a 6-6 and 332-pounder who played very well in seven starts last season. Due to injuries, he started only one other year, 2010, but he was pretty good that year. Kansas City’s Jon Asamoah, who lost his starting job to Schwartz last season, is a four-year veteran with 41 starts. He’s not bad.

The Bills have some developmental prospects at guard and they could look to the draft at interior OL, too.

Right tackle: The expectation is the Bills want an upgrade for Erik Pears, who was not that physical in the run game. A big consideration: The draft is deep at tackle. The Bills could have a chance to draft one of the top two offensive tackles in the first round. They also could get a starting-caliber tackle in the third round. They also need more depth. Chris Hairston missed all of last season with health issues. The only other backup tackles on the team are developmental prospects.

Given the draft’s depth, it seems unlikely the Bills want to get into a bidding war for one of the top free-agent tackles.

The free-agent crop is pretty good. The big-money prospects include Baltimore’s Eugene Monroe, Kansas City’s Branden Albert and Oakland’s Jared Veldheer. The Saints’ Zach Strief, who Buffalo’s Doug Marrone coached for three years in New Orleans, is hitting the market at age 30 after three strong seasons as starter. He will be expensive. Ideally, Bills General Manager Doug Whaley wants younger, ascending players.

Mid-tier guys on the free-agent pay scale could be Cincinnati’s Anthony Collins, St. Louis’ Rodger Saffold and the Jets’ Austin Howard. Saffold is interesting. After losing the left tackle job, he played six games at guard and six at tackle for the Rams last year. He probably wants to be paid like a tackle but he might be better at guard. Can he be had for a reasonable price?

Linebacker: A more physical presence in the middle will allow Kiko Alonso to run and chase from the weak-side spot. The Bills have had two physical middle linebackers in for visits in the past week – Baltimore’s Jameel McClain and Arizona’s Jasper Brinkley. Both are run-situation players. McClain, with 55 career starts, is better.

Two 32-year-old veterans, Karlos Dansby of Arizona and Daryl Smith of Baltimore, can still play. Dansby was one of the top 10 linebackers in the NFL last season. Smith, though, is smaller than Dansby and more effective against the pass than the run.

The linebacker crop is not deep. New England’s Brandon Spikes, 26, has trouble covering in space but is one of the most fearsome enforcers against the run in the league. There have been rumblings he has had disciplinary issues with the Pats, who are letting him walk. Nobody would know more about that than new Bills defensive line coach Pepper Johnson.

Younger starters on the market include: Washington’s mobile Perry Riley, who played OK in 2012 but dropped off in 2013, and Denver’s Wesley Woodyard, a pretty good weak-side guy but a finesse player.

Quarterback: Whaley said last month he was very happy with Thad Lewis as the No. 2 to EJ Manuel. Whaley didn’t rule out signing a QB, but the market isn’t very good. The biggest name is the Eagles’ Michael Vick, age 34. He’s way past his prime but he probably would represent a big, perceived threat to Manuel. Do the Bills want that?

Older veteran QBs on the market include: Josh McCown, 35, of Chicago, and Shaun Hill, 34, of Detroit.

Tight end: It appears the Bills are not going to make Scott Chandler a strong enough offer to keep him off the market. He’s 28 and coming off his most productive season, with 53 catches. Chandler arguably has played his way into a $4 million-a-year salary, which would rank him about 15th among NFL tight ends.

The Bills like the three tight ends on the current roster — Tony Moeaki, Chris Gragg and blocker Lee Smith. Moeaki, the ex-Chief signed late last season, was outstanding in 2010 and decent in 2012. He wasn’t healthy in 2011 or 2013.

There are a few intriguing young guys on the market, including Houston’s Garrett Graham (49 catches last year) and Green Bay’s Andrew Quarless (32 catches).

Do the Bills want to go with the trio on hand and look to add another prospect in the draft? We’ll find out.

Defensive end: If new defensive coordinator Jim Schwartz wants to bring someone from his old team, Detroit, he might look to edge rusher Willie Young. He’s a 28-year-old, four-year veteran. He had only three sacks last year, but he’s versatile, can rush from either edge, and is an ascending player.