In a relatively quiet offseason for the Boston Red Sox, keep an eye on the free-agent market.

Not only is Boston still in the market for a reliever at a near-bargain price, but the Red Sox will face their own free-agent issues in the coming years.

In other words, if you want to know what J.D. Martinez and Xander Bogaerts (and their agent, Scott Boras) will want after next season, watch the bidding for Bryce Harper and Manny Machado this year.

Ditto for Mookie Betts, a free agent after the 2020 season.

Chris Sale is under Boston’s control for one more year, so follow the wooing this offseason of another lefty, Dallas Keuchel.

Boston had the major league’s highest payroll last year and prices are not going down for top players.

Harper and Machado are both 26 and appear to be looking for long-term deals, in the high-$200 million to the low-$300 million range, depending on the exact length. Harper already turned down the Nationals’ offer of 10 years and $300 million.

Harper, an outfielder, batted .249 last year with an .889 OPS and 34 home runs.

Machado, a shortstop and third baseman, put up solid numbers last year: .297/.905/37.

How do they compare to Boston’s trio?

Betts, 26, batted .346 with a 1.078 OPS and 32 home runs.

Martinez, 31, batted .330/1.031 with 43 homers.

The numbers for Bogaerts, 26, were .288/.883/23.

Betts, the American League MVP, is already looking at big paydays in arbitration, even before free agency. Last season, Betts’ first of three years of arbitration eligibility, he took the rare route of an arbitration hearing instead of negotiating with Boston. The Red Sox offered $7.5 million and Betts wanted $10.5 million. Betts won the hearing.

If Betts got that kind of money after the 2017 season (.264/.803/24), what is he going to make after 2018?

Assuming Betts keeps playing at a high level, his free-agent demands will be staggering. Based on his arbitration win last year, there’s no reason to believe Betts will settle for a hometown discount or a long-term contract now, although Boston would be wise to try.

Martinez signed a five-year, $110 million contract with Boston last year, but with opt-out clauses after the 2019 and 2020 seasons. Martinez made $23.75 million last year and is scheduled to earn the same in each of the next two seasons (and $19.375 million in 2021 and 2022).

If Martinez puts up numbers like he did in 2018, Boras is sure to want his client back on the market.

Bogaerts had the third-highest OPS among major league shortstops, behind Machado and Trevor Story of Colorado. His bat may not be as valuable as Betts’ or Martinez’s, but Boston has no apparent replacement ready in the farm system.

BOSTON RAIDED its farm system to trade for Sale. Now the Red Sox must decide if they can afford to keep him beyond 2019. Sale, who turns 30 in March, is known for getting off to a dynamic start and then fading. Two stints on the disabled list last season furthered the concerns. Still, he is an elite starter and, in only 158 innings last year, recorded a 2.11 ERA and struck out 237.

Boston can gamble now – push for a contract extension and hope Sale stays healthy – or later, and wait until after next season, when the price may go up.

Prices are high for stellar left-handed starters. Patrick Corbin, 29, signed a six-year, $140 million contract with Washington. And Keuchel, 31, is fielding offers.

Last year, Corbin was 11-7 with a 3.15 ERA and 246 strikeouts in 200 innings; Keuchel 12-11, 3.74, 153 strikeouts in 204 innings.

AS FOR FREE-AGENT relievers, Boston seems content to let closer Craig Kimbrel walk. Kimbrel, 31, is reportedly looking for a deal in the $80 million range. The Red Sox, who might close with Ryan Brasier or Matt Barnes, could still use another proven arm. If they were willing to let Joe Kelly go (three years, $25 million from the Dodgers), they are likely waiting for a team-friendly deal.

After all, Boston needs to save some cash. Next offseason won’t be so quiet.