SANTA CLARA, Calif. -- The San Francisco 49ers have undoubtedly had a busy offseason. Although they elected not to go crazy with their spending in the free-agent market, they have spent plenty to re-sign some of their own and fill needs on the open market.

After signing quarterback Jimmy Garoppolo, receiver Marquise Goodwin, offensive tackle Garry Gilliam and defensive end Cassius Marsh to contract extensions, the Niners brought in cornerback Richard Sherman, center Weston Richburg, running back Jerick McKinnon, defensive end Jerry Attaochu and guard Jonathan Cooper.

Despite all of that spending, the 49ers still have plenty of cap space. According to ESPN Stats & Information, San Francisco has $42,473,184 in available cap space when accounting for 53 players. That doesn't include accounting for their rookie salary pool, which overthecap.com projects to cost $8,347,086.

Even with that substantial amount of cap space left, the 49ers seem to be mostly satisfied with what they've done in free agency. That doesn't mean they're entirely done spending, as it remains possible they could sign another veteran or two -- with another cornerback a likely addition. But for the most part, they're done.

Which begs the question: What, exactly, will they do with that cap space? The answer already can be found on the roster. With a handful of young players headed toward free agency in the next couple of years, the Niners are setting aside some money to make sure they can keep some of them.

Here's a look at the players who could be next in line for contract extensions:

DT DeForest Buckner -- The 49ers can't even technically sign Buckner to an extension until after the 2018 season and he can't be a free agent until 2020 at the earliest, but that doesn't mean he won't be a priority from the moment the Niners can sign him long term. They view Buckner as a centerpiece of their defense and expect him to keep getting better. Buckner is going to get big money when the time comes, so the sooner the 49ers can get a deal done with him, the better they can plan for having him and Garoppolo as their most expensive franchise pillars.

S Jaquiski Tartt -- Tartt needs to have a fully healthy season in 2018, but he showed the coaching staff enough in 2017 to garner belief in him as one of their starting safeties beyond next season. He can play free and strong safety in the Niners' scheme, which also gives them some versatility when determining how they want to build out the rest of the secondary around him.

OT Trent Brown -- Based on production to this point, Brown is deserving of a lucrative contract extension. Just how lucrative and how soon the 49ers are willing to pay him will depend on how he comes back from a shoulder injury. Brown has struggled with weight issues in the past and the concern is that he won't return from injury in the best of shape. That also could raise some red flags about how he'd perform once he receives a big contract. Still, Brown is as talented a pass-blocker as there is in the league, according to coach Kyle Shanahan. As long as he comes back in shape, healthy and motivated, he's in line for a contract to match his 6-foot-8, 355-pound frame.

S Jimmie Ward -- Ward is set to count more than $8 million against this year's cap as he plays under the fifth-year option from his rookie deal. The Niners have repeatedly said they have plans for Ward, and they are still believers in his fit as a free safety in coordinator Robert Saleh's defense. Alas, Ward has struggled to stay healthy, and though his versatility has value, it doesn't mean much if he can't stay on the field. With Adrian Colbert showing promise, the 49ers could move on. But if Ward does manage to stay healthy and play to the level that the 49ers believe he is capable, he could get an extension.

LB Eli Harold -- Harold was quietly an important piece in the 49ers' vastly improved run defense in 2017 while transitioning to the strongside linebacker spot. General manager John Lynch has intimated that Harold could get more pass-rushing opportunities from the Leo defensive-end spot next season. If Harold can make that move and offer some pass-rush pop, the Niners probably would be willing to keep him around.

K Robbie Gould -- At 36, Gould is much different from the rest of the players on this list in that he isn't finishing up his rookie deal and heading into the prime of his career. He is, however, coming off a terrific season in which he was many times the team's best source of offense. Gould is in the last year of the two-year contract he signed with the Niners in 2017. If he can come somewhere close to the 95 percent field goal conversion rate he had on 41 tries last season, re-upping him would be a slam dunk.

DL Arik Armstead and G Laken Tomlinson -- Armstead and Tomlinson are in the same boat in that they're entering their fourth NFL seasons as former first-round picks. Which means the Niners have a fifth-year option they must exercise by May of this year in order to keep Armstead and/or Tomlinson on a one-year deal in 2019. Neither Armstead nor Tomlinson is likely to get a long-term contract this offseason, as both have plenty to prove before the Niners can invest in them. Armstead has dealt with repeated injury issues and his fit in the scheme remains unproven. Tomlinson struggled for much of last season after coming over in trade, but the Niners liked what they saw from him near the end of the season. Armstead and Tomlinson have plenty to prove in 2018 before the Niners are going to be willing to commit to them for the long haul.