I have tried kopi luwak and IMHO it taste bad, I couldn't finish it.
I think there is one more expensive than that one and it is the Black Ivory, collected from elephants waste [1]. But after been disappointed by the kopi luwak I am not interested in expensive coffee, give me a cheap colombian like Juan Valdez, or some organic colombian.
The theory behind Kopi Luwak was that the civets knew which (coffee) berries were perfectly ripe, so ate them; in the process, pooping out the seeds (coffee beans).
Once humans found this out, now civets are kept in cavity and fed just coffee berries (i.e., they have no choice, just eat whatever is put in from of them). Natually, the beans that come out will be no different than average coffee beans. Yes, there's this whole "civet digestive enzymes" part, but that plays a negligible role IMHO.
[1]. https://en.m.wikipedia.org/wiki/Black_Ivory_Coffee