While we don't know exactly what the Giants budget will be next year, we can take a guess based on their current payroll obligations and their past opening-day payrolls.
Right now, the Giants current payroll obligations to players under contract, players eligible for arbitration and players under club control total around $120 million by my unofficial estimate (h/t baseballprospectus.com).
Those players are Pablo Sandoval, Buster Posey, Hunter Pence, Brandon Belt, Brandon Crawford, Gregor Blanco, Joaquin Arias, Hector Sanchez, Matt Cain, Madison Bumgarner, Ryan Vogelsong, Tim Lincecum, Barry Zito, Brian Wilson, Sergio Romo, Javier Lopez, Santiago Casilla, Jose Mijares and George Kontos.
Melky Cabrera, Angel Pagan, Marco Scutaro and Jeremy Affeldt are the key players eligible for free agency.
Opening-day payroll has gone from $96 million in 2010, to $118 million last season and up to $131 million this year. Given that the Giants have won the NL pennant two out of the last three seasons and selling out AT&T Park every night, there's no reason to think payroll can't increase further next year.
While we don't yet know the Giants exact payroll parameters, we know that there's room in the budget for Pence and Angel Pagan because general manager Brian Sabean said as much (via mlblogs.com) when the Giants acquired Pence. At the time, Sabean was discussing Melky Cabrera, not Pagan, but Cabrera's suspension and Pagan's hot finish make them interchangeable in my view.
We do know which players are eligible for free agency this offseason, but we don't really know what the price tag will be, and we also don't have much of an idea as to which players currently under contact will be potential trade targets. Last winter Sabean improved the team by surpassing the free-agent route to instead acquire Cabrera and Pagan via trade.
Here are five players whom I would consider replacing this winter. These players aren't players whom I think the Giants will replace, they are just five guys whom I would personally look to trade or replace if I was the general manger of the Giants.
Thankfully, Sabean is doing a fine job, so you don't have to worry.