I paid $8 for this same easy-to-follow pattern, but you can get it here for FREE with very detailed photos of each step.
The corset boning and D rings are available at most sewing/craft stores like Jo-Ann's. Besides saving a ton of money by sewing your own, you can choose from an endless array of fabrics and personalize it as much as you want. Just make sure the fabric you choose is lightweight and breathable. Also, if you're going to be using it outside in the sun at all, you may want to go for a lighter color of fabric so baby stays cool.
Even if you don't plan on breastfeeding any time soon, these make great gifts for moms-to-be. I've used mine everywhere and have been asked by several people where they could find one.
To be completely honest, because I'm not much of a seamstress, I did have some frustrating moments making this. However, after studying the pattern several times, I eventually got it, and I must say, it looks pretty good. I hope this pattern works well for you. Have fun and let me know how yours turns out. lotsalove!