Invitation Inner envelope alternatives?!

What about sheets of vellum? You can get 5x7 size in the wedding section at Hobby Lobby, and probably other craft stores. OR you could try to find other envelopes that can be purchased seperately made out of thicker paper.

You could do linings for the envelopes. Google "diy envelope liners wedding" for ideas.

Mine came with cream colored tissue paper to put on top of the invitation. I didn't like the cream color so took some that I had in my wedding color and cut it to size you could do that pretty easily and it's not expensive at all.

It'd probably be cheapest to go out a buy inexpensive outer envelopes, something at least 6" x 8".