Going through my 30+ freewheels this is what I've found:

Steel freewheels weigh between 350 and 400 grams depending on gearing. There're a few outliers, a Suntour 13-23 7s I have weighs 335, a Sachs 14-24 6s weighs 411.

A few samples:

Suntour Microlite 194g
Dura Ace 13-21 360
Dura Ace 13-21 398 I don't know why this weighs more, I double checked the weights
Helicomatic 6s 400g