What is the cheapest replacement for greenhouse glass panel

[tmasa]

The gusts cracked an acrylic roof panel on our greenhouse once again.
Is there anything cheaper than 3mm horticultural glass from a local merchant (was quoted £9 for 610x715, acrylic same size is double the price from eBay).
I use it as a shed so does not have to be transparent or retain heat, just waterproof.
Thanks

 

[nickjb]

I got a load of used greenhouse glass from Gumtree. It was £1 a pane. I think he wanted £2 for bigger pieces but we did a deal on a job lot. There was also some on eBay when I was looking. You'll need to do some cutting but that is easy enough.

If you really don't mind what it is and it doesn't need to be see through find a friendly graphics printing company and see if they have any offcuts of di-bond. Lightweight and weatherproof. Should be free or a few beer tokens.