Welcome to FOG.
about your sills, do you know someone or are you friendly with a local cabbie? they are the ones that will know where to get cheap welding done. after all their motors need to be on the road all the time. Price will depend on what kind of finish your after...pay more for an "invisible" repair ... pay less for a "war wound" type of repair. I went for the battle scar because she's that old she deserves it!
cost me £30 to have mine done on one side (hole started finger size, bit more prodding fag packet size..eventual patch is approx 8 inches x 2 inches, so it got even bigger once they had cleaned the old metal and paint away)
good luck mate, and get them sills sorted before the metal termites spread..