Are you replacing the whole thing (hardware included) or just the fabric?
Actually either way it is a job, we replaced just our fabric last year and took three of us a few hours. Two guys, and me keeping the new fabric from being drug all over the ground.
It isn't hard, but you will need tools (particularly a good pair of channel lock pliers), ladders, and multiple bodies. The hardest part, with the most potential for injury (outside of falling of the ladder removing the old or putting the new into the awning rail) is releasing and/or recoiling the torsion spring mechanism.
If you are not mechanically inclined the few hundred bucks are probably less expensive than broken fingers.
But if you want to give it a try, here are the A&E instructions.
RV Awning Repair