I got into vintage MOTU collecting about 4 years ago, and have seen a HUGE swing in asking prices on the 8 back figures. I was able to acquire a 8 back carded He-Man with a tough bubble for right at 100 when I first started collecting. When it came time to sell, he went for over 700!!!! Some sellers ask a premium for those warranty figures, and some are more reasonable. It all depends on who you deal with. I have found members of this forum to offer up some great deals at times, but others who will not budge one cent. I know this isn't giving you a straight forward answer, but it is my experience over the 4 years that I have collecting this line (my favorite toy line ever!).
I am loving your photo by the way!