There are a number of factors to consider before we can even talk about costs of a prototype so have a look at the below list and see if you can answer the criteria that the prototype company will need to know.
The number of prototypes you require will affect the cost per prototype in most cases. Typically when getting more than one part made is cheaper than just getting one. This is because all the hard work of programming has been done for the first one.
Ordering more than one prototype also gives you more ammunition to haggle the cost reduction.
Colour sometimes can add cost to the prototype, for instance black plastic could be more expensive than white or clear plastic. This price will be marginal so don’t worry about it too much about colour.
This selection should start with “do i want the prototype to be made out of metal or plastic?”. Generally most prototypes are made using either metal or plastic. The choice of material and the quality of the finish you require will lead you to a group of processes to choose from.
If your prototype has to be assembled to other parts it is important to try and select a rapid prototype that offers the best accuracy. You always have the option to select a method that is not as accurate but this gives you more material to file down yourself.
You can typically request a finish to suit your final product. Some processes will produce coarse textures and this often needs to be smoothed down.
The finish could also involve painting of the surface.
The process you finally choose will also be price dependent. Some processes cost more than others. For example in China it is cheaper to get something CNC machined than it is to get it SLS or SLA produced. In Western countries this could be the total opposite.
Finishing a part will add cost to the final prototype but this too is marginal.