You should make a comedy duo routine, and hang out in the big cities and tell jokes between the two characters once a day for an hour, and ask for tips at the end of the hour. I'm sure you'd find it a successful business! =p
I can see how dual boxing makes it hard to have money. You can't really mine a node with two characters or skin the same monster or gather same flower, etc. So money making with gathering professions doesn't really work too well, since best you can do is have one character with mining/skinning and the other with just herbalism, but you can't really have them sharing professions. And since you're getting 3x exp, you don't grind as much as if you were playing solo, so less loot/money and less chance of getting greens/blues too.
Only thing I can think of to save money is to just skip/wait on skills, and keep using the lower rank for a while. Even if your skills are behind, you probably still level faster than if you played solo due to the 3x exp and having two characters fighting.
At least until it times to buy mounts. Then you're probably screwed. With the flying mounts, at least you can do the dailies, and the normal mount got cheaper and available at level 30, so that's probably not too bad. I can imagine the level 60 mounts will be a bitch though.
Well, unless the Zhevra mount is a level 60 mount that you get in the mailbox when your 'recruiter' toon gets to 60, or something. That would probably make things a lot easier with needing just one mount.
Kinda a bit curious how the Zhevra mount works, actually.