Indirect validation rule error

Hi Guys,

I have moved onto trying to learn data validation and i have come up stuck. I have attached an example. what i would like it to do is when £5000 is selected then in the customers box it would give the list for all those allocated to £5,000 and when that is selected it will bring up the number allocated (which i will be able to do by lookup, once i have the data validation bit right)

Hope i have explained it right.

I have tried using the indirect formula, but i think i am just rubbish! any ideas?