We don't weigh ours often and we don't have a large flock, so we use a spring balance. I think it weighs up to 100kgs. They're not cheap but are a lot cheaper than a crate (ours was free
). We made a couple of A frames plus a crossbar to hang the scales from, then hang the sheep in a sling. I have a pic if you're interested. Wouldn't work with commercial-sized sheep as you have to lift the sheep to hook on the sling.
I've seen folk with mobile crates who go round weighing flocks - or at least I think that's what they're for.