its not a stupid question, its just stupid how these are priced/listed.
the only way i've been able to do this is to refresh the shop wiz, and actually go into peoples shops *the cheapest priced* and have a look at which piece they are actually selling. i suggest you do it a few times though, since once i was able to get a secret lab map piece when i was buying my 3rd set for only 38k, when its true value was actually 60k since the person priced it with the cheapest price they saw i think.
sorry i'm not more helpful, but thats the only way i know of