The actual conversion is free (unless TC has a fee to verify your current license.) You'll need at least a FAA second class medical which can run 50 to 100 dollars. And you'll need to take 2 knowledge tests, one for the differences between the Canadian commercial and the FAA commercial and one covering instrument differences. Or you can just take the regular FAA commercial and instrument writtens. Testing centers will charge you 150 for each test.
There should be a TC AC explaining the process or the FAA has guidance here. Go about half way down the page to paragraph 5-606 and -607:
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