Argh, I'm probably overthinking this question. There are at least four possible interpretations...
I think the cookies are the key here. I know that if I bought a cookie from this grocery store, exactly one cookie and nothing more and nothing less, it would cost me 2,24 STEEM. But what if I want 5 cookies, or 10 cookies, or even the entire stock of cookies? It would appear that they all count as "cookies", so I should be able to acquire as many as I want or need for the total cost of 2,34 STEEM. After all, the listings for the other items show that descriptive words indicating quantities have no effect on the price (e.g. a watermelon = one watermelon = 4,64 STEEM cost).
So based on the interpretation I'm going with, one cucumber costs 3,53 STEEM, and any higher quantity of cucumbers will be a total cost of 3,63 STEEM.
My answer: the cost of two cucumbers is 3,63 STEEM.