I have read in the comments of some of the articles here that the Colts' cap number is $1.6 million. It was my understanding (and Mike Chappell acknowledged that he had the same thought as well) that when a player is put on IR, their cap number for the season decreases (perhaps disappears completely).
If this is the case, then the Colt's cap number is now more than the previously mentioned $1.6 million, since Reggie Wayne is now on IR. That would seem to be enough money to pick up a decent free agent.
Personally, I think they should stick with what they've already got and promote one (or both) of the WR's (Griff Whalen and/or Da'Rick Rogers) from the practice squad. There's a reason why they are there--it's because the Colts see something in them. It's time to take a chance and bring them up (and perhaps replace David Reed while they're at it).