Don't hit the menu button when your in a zone, problem solved.
if your going to have an NPC charge for maps that you can readily get.... you might as well just give them to the players already. Otherwise its an annoyance. Hell I'll meet you half way just give me a menu that says "map shop"
You will end up like FF11 where the entrance fee for new players after 5-10 years is HUGE and the amount of stuff you have to do to get maps, chocobos, level past 50, new areas, airship acces, ect ect bogs down people. It's just an annoyance to have to google the npc name to get every map, or do a quest that takes 2 hours when your end game to get a map for a zone that you can google for free, or map hack even (illegal!!!!!!). Anyway I think it takes away from the fun elements of the game and adds to the "grind" aspect.