I hadn't heard of "Standout Board" but when I looked it up I remembered that I've seen that stuff at Michael's. Michael's is a great place to get small quantities of practically anything art-related, though if you're looking to buy in bulk you should go to a distributor.

Not sure if you have a Michael's nearby, but there's a store locater on their website:
http://www.michaels.com/art/online/home

I've been mounting on mat board for thirty years. You can also mount on fome core. More difficult is the method of mounting. There's heat mounting, cold mounting using a spray adhesive, Scotch PMA (positional mounting adhesive) and what I prefer for anything smaller than 16x20 print sizes is hinging with acid free framers tape hung from the back of the window overmat.

I found that mounting on an acid free mat board is very cost effective. It is a good flat surface and it will not harm your picture from acids over time. I found this video the other day on www.webpictureframes.com it shows how to mount a picture very well.

http://www.webpictureframes.com/wpfvideos.html

Tom