In an effort to free up money so they can pursue offensive upgrades, the Giants are willing to trade starter Jonathan Sanchez, according to major-league sources.

The Giants have one of the best (and most expensive) starting rotations in baseball. One rival executive projected that, including salary arbitration awards, the team’s six returning starters – Sanchez, Matt Cain, Tim Lincecum, Ryan Vogelsong, Madison Bumgarner, and Barry Zito – could combine to earn as much as $60 million in 2012. That is roughly half of the team’s payroll.

When including the bullpen – with well-compensated relievers like Brian Wilson, Jeremy Affeldt, and Javier Lopez – San Francisco is on track for perhaps the highest pitching expenditure (by percentage of payroll) of any team in the major leagues.

So if the Giants are to sign a significant hitter while maintaining a payroll around $120 million, they will probably need to part with one current starter.

Sanchez is the most expendable. He’s likely to earn around $6 million next year before becoming a free agent after the 2012 season. But his value is at a low point, coming off a season in which his walk rate peaked while he threw barely more than 100 innings because of injuries and wildness.

Sanchez performed like a No. 5 starter this season, but other teams will need to weigh whether the motivation of a contract year will help the left-hander return to the form he showed while having a career year (13-9, 3.07 ERA, 193 1/3 innings) for the champion Giants in 2010.

-- Jon Paul Morosi