The simple answer to this question is that he does not have any trade value, but simple isn't good enough. That's especially true when you're talking about a player who is still owed $43.5 million through the end of 2014. The Cubs tried hard this offseason to find some team interested in taking him and didn't have much luck. We don't know what the Cubs were really willing to pay and we don't know what they would then have accepted so we don't really know anything other than the Cubs looked into trading Alfonso Soriano and were unable to find an offer they'd accept.
What we want to do is figure out how much Soriano is expected to be worth over the final 15.5 months of his contract. That's easy enough. We can use the rest of season ZiPS to get a good idea of what's expected from him this year and we can adjust accordingly for his age thereafter. ZiPS projects 323 plate appearances the rest of the way, a .329 wOBA and 1.2 WAR. Over 550 plate appearances that's basically 2.0 WAR.
Soriano still has value, but it's not worth the contract. Then again, who expected him to be worth what he was being paid in the final few years of the contract? If you did, you don't really understand how long-term contracts work. Here's an example: $100 million spread evenly over 5 years for John Smith and an average of $5 million per win. I'm making numbers up here to give you an example.
Based on the contract the team is paying for 20 wins over 5 years, but players get worse as they age.
The beginning of the contract teams are paying less than what the player is providing while at the end it's the opposite. This is expected. Soriano's contract was no different in terms of expectations. You take the good (early years) with the bad (later years).
The rest of this season we expect 1.2 WAR from Soriano and adjusting that to a full season we get 2.0. However, he'll be a year older so we'll go with 1.5 WAR next year and 1.0 in the final year of his contract. The win value is currently $5 million and to keep things simple we'll go with $5.5 million and $6.0 million the next two years. This means Soriano is worth $6 million the rest of the season, $8.25 million next year and $6 million in 2014 for a total value of $20.25 million between now and the end of his contract.
He's not being traded today so he'll have less value than that. Let's go with the end of July as that is when a lot of trades are completed. We'll go with .7 WAR the final two months and the next two years remain the same. His overall trade value at the end of July is now $17.75 million and he'll be paid $42 million. His surplus trade value is -$24.25 million.
That's the amoung the Cubs will have to send in any trade just to get absolutely nothing in return. Money shouldn't be a concern for the Cubs when it comes to Soriano's remaining contract. I see no reason they shouldn't send along all $42 million to get a better return. If they did that, the Cubs could get a very good prospect in return.
Realistically though, teams may view Soriano more as a DH, which hurts his value to the point where the Cubs may have to send all $42 million just to get nothing in return. My guess is it's somewhere between sending $42 million, getting nothing in return and getting a very good prospect. I'd guess the Cubs could send the entire amount of the contract and get a solid B prospect in return.