How handy are you?? You can open the top of the transom and dig out all the rotted wood. After that they make a 2 part composit fill that you can poor in and make a new never rot shrik crack transom.
After which you can add a bracket. I have a I/O conversion. You will see most brackets on a I/O as people get sick of the I/O brakeing down all the time. You will not be sorry that you did!!
I hadf a guy tell me that he wanted $700 to repair the hole left after the I/O was pulled and that was if he didn't run into any problems.
I did it my self for about $100 I think it was a little less. Best thing I ever done!!
Here is a link to a site with the stuff you need. I have no idea what ther cost but this might be you answer. I would have used if I had a lot of rotted wodd but did not.
http://www.transomrepair.com/