Also, trade is disabled until the 19th due to the Guild Battle event.
What I recommend you do: Start saving up. Guild Battle Participation Rewards can give you Anu/Danu/Tartu AKA Goddesses. The general going price for them is 3 for 1 TE, because they boost the enhanced unit by 3 levels.
Other things you can sell besides rare units: Maybe other 4* units. I'm not sure about the market right now, but level 40 4*s were sellable at some point.
If you want a 5* unit, they're 2-5 TE/Pot for the inexpensive ones. You might be able to find some good deals on Fantasitrade if you don't want to wait on auctions - I found some 5*s going for 1 TE/pot. Not exactly the best-looking units in some cases, but fairly good for clearing quests and for future events.