Okay. My invites are done, but I want to be prepared as to what to expect when it comes time to put addresses on them. I would like to print a light gray color ink on the envelopes of our guests' addresses. I will go over that with a black calligraphy pen. Does anyone know of a national chain that does this... or even what sort of vendor would do this? I just don't know where to start looking. When I printed my invites, the guy at fed ex office told me that they do not print on envelopes there. I just want to be prepared for when it comes time to mail them out, to know what strategy I will be using.
Re: Printing onto envelopes
This. You can buy a perfectly adequate printer for less than $100. And the ink cartridges they come with should be enough to print your envelopes. It would cost you more than that to have them professionally printed. If you can't find a friend that will let you use their printer, this is probably your best/cheapest option.
If you really want to find a vendor, you may just have to call around to various print shops to see which ones might them. A lot may do return addresses, where its same on each envelope, but may not do them with recipient addresses, which are all different. Or check for wedding invite sites to see which ones do recipient addressing. Here's a site that offers recipient addressing if you purchase their envelopes: http://www.minted.com/envelope-addressing (I haven't used them, so I can't vouch for them). Do a google search for "recipient addressing" and you should find options.
You could call around to some local print shops, but you would need one that has a digital envelope printer, which is not always super easy to find. If you are supplying your own envelopes, the cost might not be that horrible. The hard part would be supplying them with a properly formatted address spreadsheet, which you would need to do to save the costs of having them clean it up for you.