Looks like Michael's is having a buy 1 get 1 free sale until the 7th on their frames. I really want to diy one as well, but want to use a wedding photo. I think I am going to buy the frame below and attempt to add an extra piece of glass so I can change the picture. Worth a shot at least.
I just came across this post where they said this-
We made a 12x12 sand frame... and we velcroed a smaller square frame onto the glass of the larger frame so we can easily change out the picture... you can't see the velcro once the sand is in the frame
I found her post that the frame worked out, but sadly the picture is no longer there.