سلامٌ عليكم مجددًا
in fact in Arabic we even describe things with feminine and masculine expressions, so we don't have "it" literally in Arabic. Thus, those expressions could be used with people and things, but when we use them with people we mean to express our feelings toward those people, it's a metaphorical expression. So if I say to may mum, for instance, that "You are expensive for me my mum" "أنتِ غاليةٌ عليّ يا أمي" that means I said I love her too much, that she means a lot for me. The same thing with friends or others. But when we use it with things, that could mean either this thing is expensive in terms of its price, or I love this thing so much.
The other thing, that grammer which is applied with "غالي" must be applied for "غوالي", so we remove the letter "ي" from the end of the word, it would be "أشخاصٌ غَوَالٍ" or with another form "أشخاصٌ غَالونَ", this form's not important, just for the sake of knowledge :} .
I hope it's clear now, anything else? :)