Just get a membership where you get everything for 10 bucks a month, and when you stop playing just cancel it. Saves so much money compared to buying with crowns.
why not buy a medium or large amount of crowns at one time, or find out how much a zone costs, and then how much is the next zone, etc.....then go buy that many crowns....
I'm not sure what the problem with buying areas as you come to them? If it is about buying the crowns bit by bit it is always best value to buy the largest amount you can and to buy them when they are on a deal. The best crown to dollar deals are the 60,000c for $60 ($1 for 1000c) and even better the 90,000c for $80 ($1 for 1125c).
If you decide to go for membership (access to all areas, faster energy refills, bigger backpack, longer friend list, pvp for gold and random member benefits like double pet xp etc) you can get it for $10 a month but if you will play more than 5 months of the year you might prefer the year membership for $60. That's only $5 a month and if you will play more than 5 months of the year it either cost the same as monthly (6x10) up to half as much (12x10).