NTs have tumbled down in price as of late.
bog-standards NT10s are going as cheap as £225. A more recent one for £300. Others have sold in the £350 region (but included extras).
PGA NT11s (ornate/inked) have sold for £385
Special edition black/gold or white/gold NT10s with CF boomstick have sold for £500 and £335 respectively. The £500 black/gold NT sold for that price as it had been tuned by Billy Wing.
There's some random NT11 (annoed in sickly green/white colour scheme) listed for £489 shipped from the Netherlands.
There's a DYEcam NT11 on UKScenario currently priced at £520 too.
Realistically speaking, you are looking at a big loss. You can list your Nexus NT11 for whatever you like (£500-£600 is optimistic) but you will only make a sale in the £300-£350 region, judging by recent NT transactions.