6:31pm: Castro is "first on the list of players [the Cubs] won't trade," according to a team that recently spoke to the Cubs, reports Danny Knobler of CBS Sports. Knobler also says the Cubs have told teams that they will cover as much as $45MM of the approximately $48MM remaining on Soriano's contract if the outfielder is moved (Twitter link). At least one team has already expressed interest in Dempster, tweets ESPN's Buster Olney.

1:45pm: The Cubs are letting teams know that nearly every player except Jeff Samardzija is available in trades, Bob Nightengale of USA Today reports. Some teams are already calling the 18-32 Cubs about potential deals.

"We're starting to get some early calls now," president of baseball operations Theo Epstein told Nightengale. "There might be fewer sellers than usual and a lot more buyers. This has a chance to help us. We need core players."

Starlin Castro could be obtained for two impact prospects, according to Nightengale. First baseman Bryan LaHair and starters Matt Garza and Ryan Dempster could also be acquired. The Cubs will contribute cash in a deal involving Alfonso Soriano, who earns $18MM per season through 2014.

Though Epstein's longtime team, the Red Sox, hasn't been a seller for years, Chicago GM Jed Hoyer was trading Major Leaguers for prospects as recently as last summer. He acquired Joe Wieland and Robbie Erlin from the Rangers for Mike Adams in 2011 when he was the Padres' GM.