Seems like the EU has spread out indeed!
Like Hypno says 1500 is max, although there is a trader with 2000 septims available if you get the Wizard Tower official mod. Not sure if she buys robes, though.
And like mentioned you can invest 500 if you're a master merchant, and at master all traders have 500 extra septims as well, so you could theoretically get 3000 gold for it, if that woman from the mod buys robes.