Here's what my Dad and I did on my Dakota when we had a situation almost identical to yours.
Just cut off whatever is left of the rusted flange, and put on a SPLIT FLANGE. It comes in 2 halves and bolts over the now-flangeless pipe and will act as the new flange.
We went to a local auto parts store and bought a Walker brand flange, it seemed to have the best design compared to the other split flanges we looked at.
If you live in an area where they put salt on the roads, I suggest you coat your split flange with something (we used VHT high-temp clear spraypaint) and also be sure to get stainless steel bolts, washers and nuts to put it together, so you can take it off if you need to.