Cheap is the opposite of Buy. Buy is related to Merchant. 
Rest is related to Gathering. Gathering is related to Research. Museum can be used for Research. you are likely to find Gallery in/at/on Museum. 
Cheap <--Antonym--> Buy <--RelatedTo--> Merchant 
Rest <--RelatedTo--> Gathering <--RelatedTo--> Research <--UsedFor-- Museum <--AtLocation-- Gallery 