Blonde is in Australia, so delivery from his supplier might be a tad much

Also suspect his are electronic, which are more expensive.
In the UK several suppliers do spring balance scales eg
http://www.molevalleyfarmers.com/mvf/store/products/iae-lamb-weigh-crateYou can also find them second hand on ebay, and at farm auctions, but you need to check that they weigh accurately. Take along 4 full feed sacks, so you can check weight at 25, 50, 75 and 100 kgs (or 5 sacks if yours are 20kg sacks). No use buying scales that don't work accross the range !
You would also need to check what the largest weight it will measure is.
We used one similar to this (not exactly the same) for both lambs and slaughter weight pigs.
With pigs, you need to check that it has a steadying device (makes the weigh platform rigid whilst the pig gets on it) and then you flick usually a peddle to free it for weighing.
Also with pigs, it is good to get them to wander into it when they are younger, so they are familiar with it, we used to feed them occasionally on the the paltform rigid and both doors open. That way they happily wander in, and as you get nearer to slaughter time, you can then regularly check them with no effort, pigs walks in, eats, you shut doors, let pig eat, release rigid and weigh, make rigid and open exit door, pigs wanders out.