Quote from devilquak
A.) Buying/selling anything Minecraft-related is illegal, it's on the Mojang website that you're not allowed to pay real money for things such as plugins.
B.) Bro, if you think it's that simple, you have another thing coming. It's hell trying to learn Java from scratch, and even worse hell to learn how apply it to Minecraft. I've been developing plugins for two months and I'm still not able to make what this guy wants.
Also, you should ask for this on the Bukkit forums, you'll get better replies there.
Except you could just pay for the time of the coder and not the plugin itself. That's how it generally works with paid plugins.