Gem, I would just tell the contest holder that you don't have a shop and you don't normally sell your art so that you don't have a specific tier to fall under. If you look at the other tiers and see where you think your art would fit in and go from there.
Question? How do I know what tier I am for art? I entered a contest and they want to know what tier I'm in. O.o I dunno, I usually keep my HEE art manips to myself. lol
Every single mare in my barn is up for brood 178 Send me a link, an offer and we can go from there! Not expecting a whole lot as I just want them to be used :)