What type of mushroom would be a good substitute for the Prince mushroom?
The prince mushroom, aka Agaricus augustus is in the same genus as your common grocery store button mushrooms and portobello (both Agaricus bisporus.) I'd probably grab portobellos in lieu of the prince, though they won't have the almond scent.
if you want the sweet aromas still, you might try picking up a hedgehog (sweettooth) mushroom or chanterelles...both would be great if you want to keep that aromatic quality.
Chantarelles have been abundant (and inexpensive) in California of late. FWIW the Portobella is just a fancy marketing name for the common brown mushroom. Ditto for cremini. Same mushroom at an earlier stage of maturity.