Have you used Vistaprint before? I use them a lot for little things, like labels, business cards and stuff like that. They have baby shower invites really cheap and CUTE. First set is free, actually!
http://www.vistaprint.com/gallery.aspx?pg=39&preid=51&xnav=TsrItem
The only thing with them is when you check out, just make sure you read carefully. Some people complain that there is a box auto-checked to say that you want to join their monthly club. Just uncheck it, and you have no problems. Sometimes during check-out lately, though, it hasn't shown up, so maybe they fixed the issue...lots of people complained.
Re: **Belle re: Invites**
::butting in::
I use vistaprint also, I even used them for Elise's birth announcements. They're great.
::butting out::
Ok I figured it out! I designed a very cute invite which I am quite proud of and figured out how to change the text.
Now I have another stupid question. Do they come with envelopes? It says add matching envelopes for whatever price, do I have to do that? Do they come with just plain white ones?
You can order the plain white ones. They are (obviously) cheaper than the ones that match. There should be a place for you to just add plain ones instead of matching ones.
Like Shoe said, white ones are free.
Glad you figured it out!! 
The Nifty Foodie
Life/Craft Blog