I've been buying 4 x 8 sheets of styrene for well over 20 years, in many thicknesses from .020" up. These days it's about $8.50 per .020" (0.5mm) sheet--but then I'm buying at quantity 20 or so, as a big ship eats up a lot of plastic. I scribe my own with a $180 Silhouette vinyl cutter. That cutter blade will not penetrate .020, so it leaves a ridge on either side of the cut, which I find mimics raised metal ribbing quite convincingly. I am trying to use a big Black Cat Cougar cutter, which will easily cut through .020 (and perhaps thicker), but does not like long straight cuts of 20" or more (ship decks, for example). The Cougar uses a drag blade, and I think the side forces (which can be enormous with styrene) are forcing it off line. It does a great job on the face of superstructures, with many square windows. The Silhouette will scribe a 40" x 6" deck with many openings (such as a Great Lakes freighter) without a glitch, except then it's a score-and-snap routine.
I've used .060 styrene for the fascia of the Portsmouth Branch--cheap, strong, easy to score and snap if you have strong hands.
Structural shapes from Plastruct or Evergreen have indeed skyrocketed in price. Brass shapes are now cheaper than plastic and are much finer, especially for round or square telescoping tubing. When Model Expo had their fire sale years ago, I pretty much bought their entire stock of copper and brass shapes.
I still haven't found a supplier of .010 styrene sheets. I buy from Curbell down near Cincinnati--a great place--and, when I am in Alabama, from USPlastics near Columbus OH--which has gotten me supplies within three days of ordering. USPlastics is a little more expensive per square foot, as their sheets are 40" x 72", but the shipping is inexpensive and fast. And the 40 x 72 sheets are easier to handle!
The only downside to styrene for me is that it is electrostatic, so I'm continually dusting it off.
