Thanks everyone!
CS- We bought the poly by the cubed meter. The total of mine was about 1.86 cubic meters and cost about $300. I'll double check the invoice when I get back to the workshop.
We have a total budget of $500 I should add, I'm probably already over budget by now with the paint and top-coat... But I might just eat some of those costs so I have some extra money for my third term project.
Anyway, I am now ahead of schedual! I got the basecoat sprayed on today, so the plan for next week is 2 days of washes (hopefully 4 coats) and one day of touching up with the airbrush, scenicing and building a small plinth (which I might be able to do between washes)
It actually looks way better in the photo's, I'm not very happy with the colour, I was aiming for a warmer feel, but it currently looks like cement. I'll keep messing around and hopefully I will get it to a colour I'm more happy with. But at least I now know how to texture really convincing cement.