Reddit mentions of Eating Clean: The 21-Day Plan to Detox, Fight Inflammation, and Reset Your Body

Assuming you tolerate other grains well, they're a cheap source of gluten-free calories. Aside from rice, you can cook a lot of delicious things with chickpea flour. Millet and oats can be good too, but are sometimes cross-contaminated with gluten from other grains. Local Middle Eastern/Indian/Asian shops sometimes have really good prices and a lot of gluten-free ingredients.

https://www.amazon.com/Eating-Clean-21-Day-Detox-Inflammation/dp/0544546466/ is the best gluten-free cookbook I've ever used. If your budget is ultra-tight, https://cookingonabootstrap.com/ might also be useful to you.

I'm vegan and have experimented with gluten-free food. As a general rule, the cheapest and tastiest options are the ones that happen to naturally be vegan/gluten free, not the really expensive 'fad' substitutes. Fresh fruit tastes great, Indian recipes for rice and lentils with vegetables do as well, while frozen gluten-free pizzas or supermarket gluten free cookies cost way more and don't tend to be satisfying.