So in general, larger fish cost more... but well you know they are good looking fish, plus you don't have to wait years. Of course buying adults makes tank mixing harder.
And if you buy young, well if you get females it is very hard to tell them apart... So I would suggest geting juvi males that are just starting to show color. (IE for the max color an all male tank is the best way to go.) Also try to stay away from two of the same types, or very similar coloring. While they both might eventually show color, trully when a male starts to become fully dominate, all others of its type will show at best half there color.
As for a good estimate on prices... Look at erik dykes webpage. You can find local fish in you club cheaper, though you wont get the selection unless you are lucky. (IE like today grabs, or my Exo which cost me for 4 the same price it would have cost me for 1 male.)
I would highly suggest against you local LFS, unless you know them and they aren't setting crazy prices like ours down here do. (150 for a crappy Lwanda is my best example... At the auction today 3 of my lwandas went for a buck... and given 2 years they would have been a match in looks for the ACA winner.)
Also get rid of the ruby red females... Unless you want to make just an breeder tank somewhere, and have one male really showing and the rest not.