This depends completely on how intricate your invitation will be. The cost per invitation lies between $1 and $50. Paper type and printing options will also affect the cost. Engraving and thermography both give raised print, which is more expensive than laser printing or lithography (which does not).
It will cost a lot less if invitations are hand-made but this should absolutely not be done unless you have a copious amount of time on your hands, and a creative mind. 90% of the time, the best invitations are those that are created professionally, but don’t step away from the drawing board yet. Templates may cost less than custom designs, but the latter still gives you the option on creating your ideal invitation, then asking a company to recreate it.
Be sure to order around 30 more invitations that you actually need. You’d be surprised at how even your favourite uncle might have his name misspelt, by you, in a moment of distraction.