Sure, garage conversions are not just to create bedrooms. :0) You might consider losing the garage door and adding windows. That means re-bricking the front of the house. You will have one seriously big kitchen . . . maybe expand 1/2 into garage and use the other half to expand your livingroom? Adding the garage (to the right?) is do-able if you can meet the setback requirementsof your community . . . looks like you can use the slope to minimize excavation. Would you put a basement under the garage too?
No way to estimate costs without dimensions, decisions on design, choices on windows & finishes. This will be a major remodel.