Hey Chavo, welcome aboard.
Sorry to hear about your job. A motorized bike is easy on the gas. You can use a weed eater engine; people here have done that. Check out the DIY forum (DIY Home Built Motorized Bicycle (non kit) - Bicycle Motor at Motorized Bicycle Forum
). You would be fabricating most of the parts yourself that way.
Many of the kits for sale have a china motor with a built-in gear box for a chain drive to the rear wheel. Whatever route you go, people here have lots of valuable info.