68 Barracuda floor pan rust advice

Welcome to the forum. To me, it doesn't look worth cutting out the entire section. You can probably completely plug those holes using a mig welder alone and a grinding wheel to smooth both up top and underneath. Unless it looks a whole lot worse underneath, that's the direction I would head in. Rust proof it all afterwards. Yep, I would buy a mig welder. It helps a ton on sheet metal repair.