Suppliers and types of foam polystyrene for model construction.

I'm looking for polystyrene suitable for constructing models for testing, only has to last for the duration of the test then it's rubbish. I want something that is easy to cut wing and foils from with a hot wire or Dremel.

Anyone know the cheapest and best source and what is the largest size you can get? It's not for making a boat or mold, just for making test models.

Once I know the largest supplied size then I can choose a suitable scale for my models, I want to be able to cut the wing sail from a single piece and then just mount onto the hull then test.

 

OK found out that its bloody expensive, the biggest size is 7m long by 600mm thick that is a big but the problem was the max width is 1.2m, so it looks like 1/2 scale is the largest model I can make. But $300 for the largest sheet, I am going to spend more time with CFD.

 

Polystyrene from building suppliers in 2' x 8' x 2" sheets are available here on earth but on Mars...?