hrm, I'm not sure about how much regular quinoa it would take to make a cup of flour. Not a whole lot more than a cup, maybe two. When I make it, I make a ton and store it.
Anyway, for baked goods WITHOUT yeast, I will do a 3:1 ratio (quinoa flour:ww flour (or other type of gluten flour - sorghum flour works well))(ie: 3/4 c. quinoa flour and 1/4 cup ww flour to make a full cup. You may be able to replace the entirety of the ww flour with quinoa flour. I've never done it, but I'm sure it would work ok. It might have quite a bit softer crumb because of the lack of gluten in the bread, but gluten is more important in yeast breads.
If you're making a yeast bread, the most I've ever successfully used is a 1:3 ratio (quinoa flour:ww flour). I tried more, but it just doesn't come together right. I'm sure I could experiment with different flours, but nobody in our family has a gluten intolerance, so it really isn't an issue for us. I use the quinoa for increased protein.
You can also buy quinoa in a box by the pasta. It's a little more expensive that way though. Since finding bulk grains, I hardly ever buy pre-packaged grains. They are always way more expensive. Once, I paid $4 for a 8 oz. pkg. of red lentils.....what a rip off! I won't make that mistake again.