2 cable modems in one house?

Hi Saminya, Is the Garage attached to the house, or significantly farther from the house? You can possibly consider a cheaper alternative by wiring a second router by Ethernet to extend closer to your garage, but this may make for a weaker connection and undergo more interference. Only one modem is allowed per internet account. If you're looking to have a 2nd modem in the house, it would require setting up a "roommate account". I've seen customers go this route for wanting internet in their guest house that is a significant distance from the WiFi signal.

If your garage is within 100 meters of your existing router you can run Cat-5e or Cat-6 UTP (unshielded twisted pair) between the two locations.  Maximum distance for 100BaseT or 1000BaseT (gigabit over copper) in 100m.  In the garage you will need a wireless access point, not a router, you can use a router if it's firmware allows it to be configured as an access point.  Turn off all routing functions and dhcp. Use you main router as the dhcp server.

Another idea is using Ethernet over power lines to connect your access point to the main router.  You can find power line adapters at Amazon, Newegg, etc.