In English "cheap" can mean something is either inexpensive or of poor quality. Does "goedkoop" have both meanings in Dutch? I used "inexpensive" instead of "cheap" and it was marked incorrect, so I was curious.
No, normally that doesn't exist. Plural is always with 'de'. E.g. het feest, de feesten (the party, the parties)
Perhaps with words that include a plural and don't exist in singular in Dutch? (Like het vlees (the meat), het volk (the people))