Your key is becoming less and less worth for every day, since they are adding more and more all the time. Sell it while its worth anything - if your waiting for a trade? then it could become worthless before you find any. They already mentioned that there will be a 100% realease this fall. So that means lots of beta-keys in this and next month.
Sell it for money and buy your beta key for elder scrolls for money. Well anyway, contact me if your interested. Because it prob wont be many weeks before there are lots of keys out there.
Also remember in elder srolls beta they only allow you play for the current event then they are revoked. Currently each event is one weekend, so the people that got into the first wave of invites can't even play the game anymore. Same for the people that got in for this second wave, they will only be allowed to play this weekend then the accounts will be shut down until the next event. Also these events are very specific things that they test.
So they are going to be easy obtainable for 10-60$