Not every new outfit is $18, the majority of the past new inclusions are actually about $12. Their pricing seems to be all over the place though. Some things are $18, others are $12, honestly I can't find a reason why some things are priced higher than others on that shop. One reason I don't purchase the majority of the stuff offered. I have bought stuff, but mostly on impulse - which is probably a problem of mine in itself

(mostly fantasia). I only have one store mount, and i bought it on sale when it was like $16 (account wide carbuncle - so my alt has it too!)!
I don't think they necessarily should. The cash shops in that game, or even something like ESO is completely different. By the way ESO regularly sells "limited items" such as mounts at $40+ and their big houses cost like $100, but it's buy to play with an "optional sub"!