Where are you going to find crushed rock with similar characteristics? Pumice/lava rock comes closest - or Haydite; and yes, it can be substituted, on a size for size basis, though I don't know why you would want to?? Some use Turface instead of perlite, too.

Al

There is a local crushed rock available. Not sure it will work or what its characteristics are though the size is about the same as course perlite. I would think a pumice/lava rock would be more absorbant than perlite. Thought perlite was strictly used for areation. Assuming that was the case, then I would think any crushed rock would do. Obviously I'm wrong about that.
If I could easily find a 4cf bag of perlite that was affordable, I'd buy it. The stuff I found is not course enough though the price was right. Small bags of perlite cost too much.
As for the peat, I can buy a yard of crushed pine bark locally and get 1/2 yard of fine bark and dust from screening through an 1/8" screen that could be used in place of the peat, and a lot less expensive than peat.
I'm just trying to put together a good mix that will work with what is easily available at a price I can afford.