What can I substitute for Rice flour in a gluten-free pizza?
I would go out an buy some.

Dough textures for gluten-free breads are fragile and the result of extensive testing with various non-wheat flours (at least, good ones like Serious Eats are).  None of the other flours you have available will have the same water absorbsion or starch content which rice flour does.  If you substitute, you'd have to make the recipe several times in order to recalibrate it.

Besides, rice flour is generally pretty useful if cooking for someone who can't eat gluten.  So you'll use the rest of it.  And if you can find it in a bulk foods store, it's quite cheap.