It really depends on the seller. As in, you could sell one for a few Common Crates if you'd like, though this obviously isn't a profit for the seller. On the flip side, don't expect to pay cheap for a limited Robux-exclusive hat.
Even though it's only a Legendary-tier Dominus, if I owned and were willing to sell it, I'd be expecting at least a few somewhat rare items in return. What "rare" means depends on your definition.
A Shadow Dominus is inferior in every stat except for Ore Value, which generally isn't a problem if you have a lot of rebirths or the VIP game pass. Despite this, it was priced at ~2.6032 times the price of a Patriotic Dominus.
If you haven't already, remember to keep your inventory as attractive and expansive as possible, as to entice potential clients.