Where about are you?
It really depends on what size they are, how muh you want them, how difficult they are to get hold off etc
To give you an idea, I recently paid £5 for Red/Brown Bn's and £10 for LDA16 Calico Longfin Bn's
Both circ 1.5inch long
Prior to that I got some Albino's for £2 each they were also a similar size
Are these from a local breeder or a LFS?
I do not purchase anything under this size as in the past I have had no luck with 1 inch and under as they do not seem to survive long.
The Bn's I have purchased up until now 1.5inch - 2inch have all done okay. (except the last 4 I purchased)
I am currently considering some L numbered plec from Pier they are £15-£25 each and 1.5-2inch, not quite decided which ones I want yet.