To continue, the Gift Shop had unreasonably priced gifts and the students were unable to buy from it.

unreasonably 是形容词 unreasonable 的副词形式，由前缀 un-（表示"不"）加 reason（"合理"）加后缀 -able（表示"能够"）构成，最后加上 -ly 变成副词。unreasonably 意思是"不合理地"，指价格过高、不符合常理。