My wedding invitations can be printed by 99% of the printing shops out there. I recommend printing the in the traditional way and not digital (it just looks better) but it is not a huge difference. you can even print them by 1800-postcards, Vista Print or any place you know that print postcards.
Most of the invites I did been used as a large format of postcard as it is not expensive but still very impressive. the sizes are 4×6 5×7 6×8 but again if you have a different preferences for size it is not a bid deal (as long as you mention it early on in the process of the design). the wedding invitation can even be printed as round invitations.
Printing cost can be approximately from $100-$200 for the postcard size.
Feel Free to contact me with any questions you might have about it or contact the above vendors directly.
Love Hillik