Substitute for seafood/shrimp stock for crawfish étouffée?

Combination of bottled clam juice and water.

check the frozen section for shrimp or small crabs that will be cheaper than $9/lb also?

I used clam juice once and found I didn't care for the flavor and it was too sweet for me. I've used chicken broth on a number of occasions, either homemade, Swanson's or BTB (watch the salt on this one) or Minor's. I've also used Minor's shrimp base which works. I order that. Last week, I made it and used Glace de Fruits de Mer Gold which worked better than anything I've ever used. I just used a tablespoon in water.

This is what it looks like.

LINK

You can find it in kitchen shops or the finer grocery stores. Places like Whole Foods likely carry it, as well. It doesn't need refrigeration unopened, but I keep it in the freezer.