Can we now with the new setup quit Merana's quests, if they are too expensive?

you can't quit, but you can just not do it and let the timer run out and the quest will be forfeit. i think she's around for 12 hours at a time, so at the end of that period, she will disappear and so will the quest.

Ah, thank you. I didn't know there was a timer now and the quest expires. Just as good as being able to quit! With the old quests you could be stuck with excessively expensive ingredients for the rest of your life, if you were unlucky.