We keep a rather comprehensive list here:
The closest I see on there are Grenada, MS and Houston, TX which are both quite a distance.
For 1lb foam in Iowa where I'm located it's available for under $200, and 2lb foam for a little over $300 plus shipping. Sometimes there are higher prices for 1 qty, and price breaks for higher quantities that are worth asking your block molder about. Also the prices do fluctuate with petroleum prices as Polystyrene is made from a combination of Ethylene and Benzene which are petroleum based products.