I make gold off these frequently. I can usually pick up the Fiery ink off the AH for around 3g each. These inks are mainly used for Darkmoon Faire Card making, but while leveling, Inscriptionsts will get more then they need to level. I also trade ink for Celestial Ink (Ink of the Sea costs me about 1g to make each one)
These Vellum’s sell normally for 12g+ on my server which is a nice profit margin. I usually don’t list more than 10, since they are not a daily use item like flasks or pots, I rarely sell all 10 every other day.