You started looking for invitations, you have no idea how much they should cost ...
According to TheWeddingReport.com, invitations make up 3% of a wedding budget. So if you plan on spending $28000 on your wedding, a good rule of thumb would be to plan on spending $800-$900 on stationery.
In the end, it all depends on what you want and feel comfortable spending.
I wrote an entire article on this subject on our website.