The prospect cost for the Tigers would be too high to make a difference this season
The problem the Tigers have is that, at present, this is a very flawed roster. The offense is a bottom five unit in all of baseball by fWAR and the pitching staff hasn't been much better. Again, it is already kind of a miracle that the Tigers are within spitting distance of the lead in the division at all.
As a result, the types of guys that Detroit would need to add at the trade deadline are the really high impact names and those guys are going to be both expensive and in high demand. If we are being honest with ourselves, it is probably going to take more than one impact move to move the needle and that is where things get sticky.
Any trade deadline this year that involves adding multiple impact players is likely to basically clean out the Tigers farm system. If you think that teams are not going to basically demand Colt Keith, one of the more exciting hitting prospects in all of baseball this year, for any of the higher end guys on the trade market that aren't relievers, you are delusional.
If the Tigers were in first place with a lead or if they were just one bat or one bullpen arm away, it would be a different story. However, the roster would also be in much better shape in those hypotheticals. Standing pat should keep Detroit hanging around while not mortgaging their future. It may not work out, but it doesn't really cost them anything that they were expecting from this season if it doesn't.