how about using the polypots. Like a black plaggy bag with holes in. various places sell them including my favourite NA Kays & they are relativeley cheap. I use them for Tomatoes for outr plants sales & the 3" pot size are around £2 for 100 (£12 for 1000 if your really keen

).
Also I've got all my colleagues trained & I often get into work to be met by a bag fullof pots & trays that they have saved for me