In 3D printing size definitely does matter, it will make a big difference. If you decrease the size of your print then all three dimensions will be decreased. This will, of course, lead to the print becoming cheaper. If you want to create a model at the height of 15 centimeter you would have to pay 150 dollars. But, if you reduce the height by 50 percent the 3D print will not cost half of the earlier mentioned price. Instead the new price would be around one-eighth of the original one, so about 17 dollars. How good is that?!
If you want to order the same piece multiple times you could profit from a quantity discount. This benefit will only be applicable as of two similar objects and will increase with every next copy. It is, of course, possible to order several prints of your 3D design. You just have to adjust the quantity counter to do this, which is thus very easy to do. Ordering several identical prints will have a big impact on the price, but this is to your advantage. You will namely have to pay less money for the second, third, fourth, et cetera copy.
3D printing can be done with a wide range of materials. Each material comes with its own price, therefore it is very important to compare prices between materials. If you are not dead set on a specific material then this is definitely a very smart thing to do. However, you should not only compare the prices. You should also compare the materials based on their characteristics and finishes. You can do this by searching for materials on Google. There are loads of useful websites that provide you with information about 3D printing materials that can be used.