just to clarify.
"plants are not the same price though"
does this mean that plant 1 plug is different price to plant 2 plug, or that all plugs for any plant are the same price, and all 9cm pots of any plant are the same price, but different to the plug price ?
in which case what is your discount, 15p or 15% or what ?
are you uk based ? feel free to call me if that would help.