Recently a friend of mine had a sweet baby boy and I made her a nursing cover up using the directions I found here. I had the boning and D-rings already because I had every intention of making one for myself when The Entertainer was born but didn't get around to it. Can't imagine that.
It's been a loooong time since I sat down at the sewing machine but it was very quick and easy to do. You simply take a yard of fabric, cut a strip lengthwise for the straps (although I agree with the author of the tutorial that the straps are still way too long). Hem around three edges, sew your straps up, add the D-rings, add the boning and voila. It's very modest and portable.