This isn't somewhere you will need to scrimp, but without having an limitless budget like Paris Hilton, don't be concerned. You may still design an attractive invitation without emptying your wallet, but be ready to spend time!
One method to do that is to produce a card template using Ms Word or whatever word-processing software you've on your pc. The simplest method of doing this really is most likely to look for something similar to "free Ms Word card templates" or "free Ms Word invitation templates" on the web. You need to find plenty of options, and Microsoft itself offers free templates.