Need some advice on charging for painting miniatures

[Just a few orcs]

Irregular Minatures do 54mm redcoats and Zulus.  Not the best Minis in the world , but would paint up nicely as "Toy Soldiers"

I suggest that you do it on the You buy me a figure for each one I paint.  That way you get figures for free and you are effectively charging Family rates for painting. I would also specify that there is not defined timescale for you to complete.  Also it effectively doubles his cost so he is less likely to want you to paint forever.