A while ago I've collaborated with the lovely Sultana and made these custom paper sleeves for her. I've made the sleeves as well as some engraved wooden airplanes, while Sultana took care of the actual invitation insert herself. This is something I often do. I call it "semi-diy" - a process which allows the bride and groom (or someone crafty who is willing to help out) to do some of the work for the invitations themselves, while the work which requires specialist equipment is done by the designer who owns it.
In this case the client requested paper sleeves with a map of a specific area. I was able to buy a digital file via the Internet to use for the initial layout of the sleeve. The map design was digitally printed on paper and then die-cut and assembled by me at home. I've also engraved some of my wooden airplane charms with the names of the bride and groom, before the parcel was sent to Sultana to do the inserts and assembly.
The semi-diy option is great if you're on a tight budget and have the necessary skills and patience to do the computer layout, printing, cutting and assembly yourself. I would, however, like to advise that you should never underestimate the work involved in making invitations. I know of brides who started out with making their own invitations to save money and ended up so unhappy with the results that they threw everything away and ordered invitations from a professional designer! (And of course the implication is that they've paid more than what they would have if they went to a professional straight away!)