You would have to get actual estimates. I got an estimate of 6000$ to put in a new single garage door in a garage wall that had no door. They would have to open it up, put in new headers, do concrete, and the garage door and operator. It depends on what is needed, if electrical needs rerouting etc.

Is the garage floor sloped to a drain, or does it slope to the door for snow melt, etc to run out and not pool against a wall?

There are all kinds of bearing wall issues you will face with this, requiring the services of a structural engineer. Even is this was simple -- and it's not -- costs for things like this vary widely across the U.S. You shouldn't rely on this forum to give you a reliable answer. Depending on the design of the house, the structural issues, the slope of the lot, etc., this could be $10K or $50K. You will be best served by getting local estimates.