How much are antique scales worth?

There really is not a lot of information to help answer this question, but I will try.
It would help to know the type, a description, age, condition, etc.

When you say 'antique scales', I am thinking you are asking about either, a). the type scales used with gram weights to measure weight, sits flat on the table.. or b) a type I just ran across recently, antique Japanese hanging Opium scale, cleverly disquised inside a wooden elephant carving.

These type scales as you can see, can have many different uses and types. The worth of the item would depend on the rarity of the item. If we were discussing the table scale. Most people probably would have seen one of these at on time or another. The other, is a rare item. Most of these have been destroyed or lost. This one was purchased in Japan by a woman who had no idea the apparatus was in the wooden elephant at the time.

Remember, the scarcity would be key here. The opium scale has a story behind it and is much more rare than the table scale. I believe it to be older as well. It would be worth more.
I wish I could help you with your item, but I certainly don't want to give you the wrong amount without knowing what you have.