I can't help with pricing. I don't believe this is an ACEO. ACEOs are only 2.5x3.5" - always.
However, if you're seeking to sell on eBay, my advice in selling art is to price your art at a price that you are willing to sell for never price your work at a price that you would regret selling it for.
~Jillian
artist, Jillian Crider
... google me!