Translation:The tea is cheap there.
I think this should be accepted. The "這裡…"/"這里…" exercise accepts "This place's…", so "That place's…" should be accepted here to be consistent.
It may be worth noting that "place" is part of the translations used in a recent Yoyo Chinese lesson on YouTube: https://www.youtube.com/watch?v=4CavUBQwOyA.
Edit: This is still rejected as of 2018-04-08.
Either one works, i think it's technically more correct to add the pronoun, but in modern English we don't require such heavy use it. An example would be "Which way is the best?" and "Which way is best?", technically the furst is more grammatical, but the second is the most common to hear
I looked up bian4yi2 on Pleco, and it said that it's a literary adjective meaning convenient or advantageous. Is the word more commonly used to mean cheap in some dialects of Mandarin?
EDIT: According to Pleco, the character 便 can be pronounced as either pian2 or bian4. So the word 便宜 can be pronounced as either pian2yi5, meaning cheap, or bian4yi2, which is a literary adjective meaning convenient or advantageous.
However, the issue is that even though the pronunciation of the sentence is correct, when you hover over the characters in 便宜, they're pronounced like bian4yi2.