you have a telephone line, dont't you, it passes below the patio? just tie the network cable to it and pull from the another end. the tie must be smood and with duck tape to make it like the continuation of the line.

you can get a old router SMC barricade sheap, get a 25 meters of network cable, connect the cable to the linksys, on the another end (office) connect the router, create a sub-network and thats it. spend $100, or less.