reuse your plastic
 

Black, blue and green plastic boxes from meat, mushrooms etc. make great seed trays, just wash with warm soapy water and dry first.
Also just seen on tv a greenhouse made from clear 2ltr bottles with the bottoms cut off and stacked with a bamboo cane through the bottle top opening down through all the bottles. Several of these were put together and connected. Would make a great cold frame!

bottle cold frame
 

That's a deadly idea! I'll definitely have to give that one a go. Thanks! Mandolin.