If it was mine I would set it up on my steel welding bench brace it up in a jig so its all in the right position then weld it up, weld in a cross brace like the new frames all fixed and I can't see where that would cost that much unless you have to buy a welder, once set up it won't take long to do the welding, small mig welders are cheap these days, I brought a decent one for $500 to replace my old stick welder and have already fixed up a mate's Norton frame one small crack and weld in a side stand mount and if done right the weld will be stronger than the frame metal.
Once the weld has been cleaned up no one will ever know its been fixed except for the new cross brace added.
Ashley