Efficient Ways To Pay To Win

Nothing in the cash shop really, unless there is some a amazing deal like cubes/scrolls for something like 50-80% off, which happens once in a blue moon and never returns. Trading items or mesos for nx is probably the most "efficient", but it is against the ToU and you could get scammed. Unless you have good gear and you want to take advantage of a cubing or scroll event, not much really.