Have you ever thought about how to print your own invitations? I think that some parties and occasions have such simply printed invitations that it would be really easy to do it yourself. Of course you would need a decent printer and some good card stock paper but that should not be that hard to get hold of. There are lots of computer programs these days which have templates and designs for cards so you would not even have to be that creative yourself.
You can even look up wording and/or poems on the Internet so you do not have to think about what to put inside. It is a really good way to personalise a card and save money at the same time. It is likely that the invites will be more appreciated too which is always nice and it is likely that some people will not even be able to tell the difference. It is worth experimenting to get the right look and style but that should not take too long and think how rewarding it will be when you produce something of a professional quality which saves you a lot of money and gives you great satisfaction.