I grew and sold mostly Alpines, dwarf bulbs and Sempervivums. The bigger perennials were in bigger pots and sold for more depending on size and rarity. Decent coloured hellebores for example went for £3. But this was a few years back, I have not done a plant sale for a long time now. In fact not since my 'escort' went to University.
One other point, if you are potting up your plants, get started as soon as possible, so that they have settled down and begun to regrow before the sale. Otherwise they just look as if you have wrenched them from the ground.