KH frame are made of 7005 T6 aluminium, T6 means they receive an heat treatment after welding in order to improve strengh at the welds. If you get it repeared, I guess it will remain weak. I would prefer to replace the frame for the latest design
First off, $40 bucks is reasonable for a quality weld, Which includes metal prep and set up with the correct weld filler rod. Typically about $80- $120 an hour at a shop. (Not everyone who welds has the correct equiptment)
Second, Because of the properties of 7005 alloy, Yes a solution heat treat process is normally done to bring it up to T6 temper. But a repair weld on a heat treated frame will be strong enough, and most likely bend in failure the next time if it is not quench cooled after weld, but allowed to cool by itself on its own time. (important) Becuse rapid cooling makes the aluminum. Dead Soft (Annealed)
With this said, only repair if you like this frame and Money/Cost, is an issue!