Best way to add an opening to garage

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I have an oversized 1 car garage, 42" between the exterior corner and house. I recently acquired a gently used Toro lawn mower that does not fit between the two although the deck comes off relatively easy. 

An overhead door would be perfect but as we are still considering this a possibly longer term flip house, I can't justify that expense. 

Is there a way to put a 48" opening with a secure door onto the side that would be cheap enough to do without compromising the structure? 

Thanks!