I have no welding training but I've used a Harbor Freight MIG welder before and was not impressed.
If you can afford to have someone do it for you, I would pay to have it done. If not, cut out the bad stuff, treat it with rust inhibitor, then pop rivet the new part in. The rivet head can be sanded flatter (not enough to cut them out) and counter sunk with a ball peen hammer, then hidden with plastic body filler. Since I live in NE Ohio, I've had a lot of experience in this process.
I would definitely fix it right away. With everything your doing with your car, how can you ignore it?
Jeff