"The food there is good but expensive."
Translation:اَلْأَكْل هُناك طَيِّب لٰكِنّ غالي.
Well, typically if we would start with Hunák (هناك), the sentence would be like this: هناك، الأكل طيب لكن غالي. A comma is added here. Not sure how to explain it but it's about how to read it. In fact, you can even put it at the end of the sentence as well. Not sure what model does Duolingo use, but probably by virtue of programming, they can't encounter or consider all possibilities? So they have to stick with one version of the sentence (my guessing only). However, in Arabic, even though not a definite rule, but usually the thing that you want to bring an attention to, is brought first in the sentence. For example, if the conversation was about a specific place, then yes, you would start with Hunák to bring the attention about that place and then you tell what is going on or what is wrong with this place over there. If your conversation was about food specifically and you want to bring attention to it, then the sentence would be like above (or even with Hunák at the end of the sentence). So, it's about the flow of the conversation; Otherwise, your answer, and the others, are all correct.
Well, طيب is somewhat used for food at times but a better expression would be لذيذ (laDíD) or شهي (šahiy). So, in some sense, yeah you can use "good" (جيد) to mark the food as being good. جيد is more general than طيب.
On the other hand, طيب can also mean kind or nice so personally I would encourage people not use such adjective to describe a tasty food, and rather use لذيذ or شهي to mark a delicious food. But well, it's Duolingo after all and I have no say in this.