Want plasma cutter, but no power hookup

There is never any need to go to a bigger gauge extension cord than what you have in the wall. For instance most dryers run on a 30A breaker with a 10ga wire size. The rule of thumb is to go up a guage for every 100ft of wire ran. Since that plasma cutter runs on 25A, you'll be fine. If it was 40A then you'd most likely be SOL as far as running it off the dryer circuit goes.