I think the price is pretty much the same regardless of the number of trays you are given (unless you go with Invisalign Express - 10 trays or less total - that was quoted to me at half the price essentially). Three refinements are included in the price I paid, but I think the number of available refinements varies from country to country. So, theoretically, extra refinements might cost extra. Also, some orthos include retainers and retainer follow-up in the initial cost, while others don't, so you could see a variation in price there, as well.
Also, losing a tray is a special case, although my ortho would not charge extra for it unless I lost them on a regular basis.
