I looked in the diy store last night and saw two blades suitable for cutting 3mm steel.
One was 7 inch and the other about 10 inch.
Prices ranged from 20 to 30 pounds.
The glossy video they were showing depicted the balde cutting through an RSJ.
I already have a chop mitre saw with all the markings, so its just a guess to how long it will last.
Happyjo