how bad is this rust?

you could do this your self for the cost of a donar rail and the the consumables for the welder. but you know how it goes. you start the rail and your going to find more rust. i dont see why you couldnt get a rail out of a parts car and then drill out the spot welds on yours and put it up and weld the new one in. i would give it a shot if it was me. i would pull the engine and entire front suspension first though.