Tue Jun 13, 2006 12:39 pm
			
			
			
			
			You're right, new metal is the only way to fix rust properly. Filler may stop it leaking temporarily, but it will continue to corrode so when you do come round to fixing it properly, the problem is even worse. Best get new metal in there as soon as you can. 
Price will depend on the size/shape of the hole and accessability etc. Outer arches are a bit funny as they need to be cut right, new arches welded in, ground down, sprayed etc etc, and also the fuel filler pipe runs through the driver's side rear arch. Some bodyshops would insist on removing this for safety which only adds to the labour I'm afraid. 
I had two 3-4" diameter holes welded up with new metal, on the inner rear arch which came to around £115. They didn't remove the fuel filler pipe and I sprayed the work myself as it was behind the boot trim.