Well as another drop down option, There should be a "Guild Bank" and when you click it, up comes one of those popups like the CE Market but as a guild bank one instead.
On it can be 3 options - Guild, Personal, Prize!
Guild
This would be a little bank which anyone in the guild would be able to use, and the GM chooses a Maximum that can be taken over a period of time to stop thieves running off with all the money. It would also be useful for helping the people in need of the crowns for gear and stuff. Also when taking money out there would be another icon which will either have a Red numbers or Yellow numbers. Red is how much you've taken out and how much you would owe the bank, Yellow is how much you put into it for other people.
Personal
This would be like a loan sort of thing for 1 to 1 guild Loans. Where when you give someone money to borrow and you can pay back slowly how much you owe through another icon and would work like that.
Prize
The prize part is something that would calculate a random average number between people in the guilds wealth.
And every week it calculates the number that has to be input into the bank for the whole guild to recieve a prize. The prizes would become bound and it wouldnt be something to awesome an dexpensive yet something to cheap that nobody wants.
It's been suggested before, you might want to start using the search bar.
Also something like this would never work, why have a bank to put stuff in when you have unlimited storage space in your knight?
( I don't need a guild bank to give me loans 'cause Chrizmaniac is my loaner ^.^)