A competent plumber should be able to figure out how complicated this would be without anything being torn out. It could be very easy or could be incredibly complex and expensive. Tapping into existing plumbing to run supply lines is one thing; figuring out how to tie into an existing sewer line is another. Without details it’s impossible to say here.

but wish we had in the garage

Where in the garage?

You posted a floor plan a few months ago -- is it the house? Do you have the 3rd garage bay?

Yes that’s correct - third garage bay would be an ideal place. The hot water heater is in the back left of that bay.

The hot water heater is in the back left of that bay.

Then you have hot and cold water, and an easily accessible drain under the sink in the bathroom.

Just get some quotes and ask detailed questions about your concerns. No one will be able to help much without seeing it in person. My uninformed guess is 2-4k if it were in my city and the whole home isn't on a slab. It's great that the water hookups are easy because that potentially saves a lot.

It looks very feasible, since you appear to have drain connections and water supply pipes nearby, but it still won't be cheap if they have to start running pipes through walls to make the connections.

Also, what is your climate? Is there any risk of exposed pipes freezing in the garage?

Bruce