I would say that a FileMaker Value list is unwieldy for long lists of values--no matter what format is specified for the value list. I'd recommend either some type of conditional value list scheme that filters the list down to a shorter list of matching values or some sort of script based system--a selection portal would be one such option.
But it seems that you need to select an ID based on two values: "costcode" and "Price". In the table from which you are looking up rates, Does combining the values of the costcode and price fields produce a unique value? If so, then your relationship should work. If not, then you have a more basic problem to solve. How, just by looking at the data available, would you know which of these rates to select-say if you were just doing this as a paper and pencil excersize?
Let's assume that Price is not unique, but the combination of cost code and price is unique. If so, then you can enter or select the price, then use a conditional value list to list only the cost codes that match that price--but this still leaves me wondering how you would tell which cost code is the correct one to select since this value is just a number apparently.
Yeah, couldn't do it with a dropdown. Ended up using a selection portal in a popover window and scripted it.
Thanks for the input.