Coin scales, a very expensive collectible. Coin scales are used in the whole world. Some of the rarest and nicest come from  Holland, Austria, France, England and Germany. Some very nice rocker and coin wipes are also to find inside the USA. You can find them with prices between 100 $ and 10.000 $.... and more. Not easy to find with original weights. Often mixed with weights from other scales. The Picture show one of the rarest scales with a value from 5.000 to 10.000 $ ( Holland )
Egg scales are a great collectible in the USA. In Europe hard to find. I saw them with a value from 20 to 300 $. The picture show one of the common egg scales.
Scales for analysis / pharmacy or assay scales. You need some place to display them, they are very technical and from high precision. To find in Europe and in the USA. If you like to collect this kind of scales, be carefull and proof each scale of the function. Often some parts lost !!! This scales have a value from 200 to 1.000 $
Letter scales are a never ending story. I know some collections from over 800 different letter scales. The rarest, you find in England. They are small and very nice and do not need much place to display. BUT it is easy to run out of money !!! The common scales, have a value of 30 to 150 $ but it is easy to spend 1.000 or 2.000 $ for a very rare one. Some reproductions on the market !!!
Kitchen scales is maybe more a German or European collectible. I am not sure about. I saw a lot English scales but the nicest, so I think, you find in Germany. I know about 1000... different faced scales. Enamel, iron, brass porcelain and tin. The value is about 80 to 250 $ rare one up to 600 $.
Grain tester is an popular hobby. To find in the USA in England, Russian, Austria, Holland and Germany. The nicest to find in Austria and England. In Germany you find the technical ones. Not easy to know how to use them ... The Picture show a Dutch one. Complete. The value moves from 150 to 800 $. Very early or rare scales arrive often an higher price.
Asian or opium weights, I think maybe the nicest weights of the world. To find from 2 gram up to 16.000 gram. They look like ducks, beasts, lions, horses, snakes, and much more..... Lots of fakes on the markets. 50-90 % are fake. If you find a set of this weights it is to 90 % fake. Is the set anything other than a duck than it is to 95 % fake. Contact a collector, if you do not know anything about this weights, before you start to collect them. The value is about 25 to 80 $ for ducks up to 320 gram. Other animales have a value from 50 to 500 $ and the bigger one have a value from 300 to 8.000 $
Weights... oh... I can not say anything in short words. Each country have their own weights. As example: In Germany they use before 1858 in each town a other weight measure. So you can only collect German weights and find never a end. The Picture show a set of English inspector weights from 1 lb to 56 lb. I love to collect them in each size. Over the value is nothing to say. You can buy them for 1 or 1.000 $. To see the value of a old weight is not easy.
Antiquity weights Roman, Syria, Greek ... fantastic weights. My wife ask me often how to know, is it a weight or anything else. You have to buy them by serious dealers. They are sometimes not nice, but they have anything ... it is a feeling.
Nested weights, super, maybe the queen of the weights. Weights insert in a house. What a great work. The oldest one are made in Nuremberg in the 15 / 16 century. In Nuremberg they was made for the whole world. Also you can find some rare old Roman, French and English nested weights. Attention, very much good reproductions on the market. In Portugal they start to copy them before over 200 years. To find from 8 oz up to 64 pound