49ers working to keep free agents but lack building blocks

SANTA CLARA, Calif. -- In the midst of a busy Monday of what will be a frenetic week for the San Francisco 49ers when it comes to roster moves, the team announced that it had signed linebacker Ray-Ray Armstrong to a two-year contract extension.

Armstrong only played in two games before suffering a season-ending chest injury but apparently showed the organization enough to earn a longer stay by the bay. While Armstrong showed some signs of being a helpful piece, he's far from a franchise building block or even a guaranteed starter.

With Armstrong in tow and extensions done for outside linebacker Tank Carradine and tight end Vance McDonald, it seems the Niners are trying to lock up some of their forthcoming free agents regardless of how much or little they've produced. Remember, the Niners -- like every other team in the NFL -- must meet a minimum salary-cap spend. They are currently on pace to have an exorbitant amount of space heading into next year.

General manager Trent Baalke recently said the team was working on more extensions after signing McDonald. None of their pending free agents would probably move the needle much if they hit the open market. So are any of them worth prioritizing? Which of them should be next in line, if at all?

Here's a look at four upcoming unrestricted free agents the Niners should be willing to keep so long as the price is reasonable:

WR Jeremy Kerley -- Kerley isn't a No. 1 receiver but became this team's best wideout the day he arrived in Santa Clara. His numbers are modest but he's shown an understanding and ability to get open in coach Chip Kelly's offense. The Niners absolutely must upgrade on the perimeter this offseason but keeping Kerley around as a complementary piece would be wise, especially given Bruce Ellington's propensity for injury. It's also unlikely Kerley will cost much.

DT Glenn Dorsey -- San Francisco's run defense has been the worst in the league for most of the season but there was a little bit of an uptick when Dorsey finally was healthy enough to play substantial snaps. He's clearly the best nose tackle on the roster. While the Niners could use more help at the position, especially after losing Ian Williams, Dorsey is similar to Kerley in that he's a solid veteran with some leadership ability who won't break the bank because of his injury history.

K Phil Dawson -- Dawson will be 42 next month and though he's showed some recent signs of wear, he remains one of the most consistent and accurate kickers in NFL history. Kelly raves about Dawson's preparation and work ethic and trusts Dawson in just about any situation. Finding a good kicker is easier said than done so as long as Dawson wants to return, it seems the Niners would be willing to have him.

A quarterback -- The Niners have four quarterbacks in the building now in Colin Kaepernick, Blaine Gabbert, Christian Ponder and Thaddeus Lewis. All four could be unrestricted free agents after the season if Kaepernick does as expected and opts out of his modified contract. The cost for any of these four will likely vary. but it's hard to see there being much of a market for any of them. In other words, some of them will be more valuable to San Francisco than others if only because of a knowledge of Kelly's scheme. There's no position more important for the Niners to improve on the roster, and that has to be the priority, but it's also probably not a good idea to go into next season with an entirely revamped quarterback room. Even just hanging on to Lewis and/or Ponder for depth while upgrading the top of the depth chart would be a logical move.