Have you tried taking the item to one of the "fences" you meet along the way within the Theives Guild questline? My question though is why would you want to sell that?
Because if you already have one you have little use for a second one.
OP, other than the speechcraft investment, or the thieves guild vendors the only way I have come up with is to buy out a merchant until they have enough gold to buy the high value item, then sell that to them and get all your money back, and sell the stuff you bought to another vendor. You just need save, test that out, and see if you make a profit. It might be that the difference in buying and selling prices cancels your profit so you'll want to reload. If you have smithing leveled up then I would suggest doing this with ore that you should be able to craft into profitable items (or if you are leveling alchemy or enchanting then stripping a vendor of those mats might be worthwhile as well.