Doug

Honestly, running the cable is the easiest, best, and least costly, way to achieve your goals.
You'll probably need a total of 75' feet of ethernet cable, and that can be purchased with the connector ends already installed.
Next you need a WAP, "wireless access point". This is a small plastic box that will be mounted in your garage. Connect one end of the ethernet cable to the WAP, and one end to the back of your router, there should be multiple access ports available.
Your router will ask for permission to use the WAP, and there may be a "passcode" that came with the WAP, and one should have come with your router. Depending on your house computer setup, you may need to enter both passcodes, or just the WAP. Your computer will prompt you.
Regardless of how you do it, remember to establish the security protocols. wifi might have some problems going through walls, but that signal can travel at least 200', from personal experience, in open air. If you live in the country, no problem. If you're more urban, there are a lot of houses within 200'.
It sounds daunting, but it's not.