I was doing my weekly ritual of window e-shopping yoga clothes (not that I really need to buy anymore) and noticed that Athleta carries maternity pants. Prices range from $69-79, which is about what they charge for their regular pants.
There aren’t very many reviews on their site to say whether they’re worth it or not, but they do have a good return policy if they don’t work out.
I will say though, of my Athleta pants, I kept wearing my Chaturanga capris throughout my last pregnancy, and the waistband didn’t cut into my belly. Something to keep in mind if you don’t want to buy separate maternity yoga pants.