To make your invitations more personal and less expensive, do them yourself. There are a number of paper stores and websites available where you can find original ideas and ways to make your own invitations.
Order your invitations over the Internet instead of a printing shop (it's a little cheaper). Mail order is another possibility.
Order a plain invitation from a company and decorate it yourself. All you need is a hole-puncher and some ribbon and/or parchment paper.