Where are the cheapest gluten-free foods?

I am intolerant of all grains and legumes but I am OK with dairy and nuts. I find cassava flour (tapioca) very useful. It makes very crisp biscuits. But it is bread I miss, and I cannot tolerate even gluten-free breads.
So I was delighted when a friend gave me this recipe:
3 heaped tblsp cassava flour (= tapioca, manioc), stir in ¼ teasp soda bicarb, ½ teasp cream of tartar, optional 1 flat teasp xanthan gum
Blend cottage cheese (a small pot), 1 egg, 2oz/60gm softened butter and mix gently into dry ingredients, adding more flour if necessary.
For bread buns put dessertspoonfuls on oiled tray, in hot oven (200˚C) for 10 minutes.
Or cook as a loaf in a bread pan at 180˚C for longer, perhaps 20 minutes.
This has a wonderful texture. It is too dry to eat by the next day, but freshens up if toasted, or just heated briefly. You can slice and freeze, and toast from frozen. You can keep half the dough in the fridge for next day.
Grain-free, yeast-free, legume-free, dairy-free, egg-free bread:
I tried substituting cooked potato for the cottage cheese, and oil for the butter, to see if this bread could be adapted for those who also need dairy-free. It turned out well, with a very crisp crust. I tried it again, this time without the egg too, and it was acceptable, though more biscuit-like, rather flat and extremely crisp:
1 tblsp cassava flour, ¼ teasp bicarb, ½ teasp cream of tartar
blend 3 or 4 pieces of potato with 2 tblsp oil
Substitutes for the cottage cheese or potato: pureed banana, carrots or similar – something to hold some moisture; tofu if you can eat legumes.
Mix and make bread buns as above; slice leftover buns ready for toasting as they may be too hard to cut by next day.
Gluten provides a molecular framework so wheat holds the carbon dioxide provided by yeast. We have to find substitutes. Egg helps rising, but too much makes a cake-y texture. Tapioca is a sticky and elastic equivalent to a gluten flour, holding the gas from the bicarb and cream of tartar, but this mixture is more unstable than wheat and yeast: mix gently and put into a hot oven quickly. Sago flour and potato flour are similar to tapioca, and can be substituted or combined. I tried coconut flour several ways and disliked the taste and texture. Xanthan gum helps gluten-free flours to bind together, helping it rise and giving it spring.
High protein bread:
If you can eat them, add a tblsp dried milk, a tblsp ground almonds, toasted sesame seeds or tahini (sesame seed paste), or toasted chopped hazel or other nuts or seeds to taste. They make interesting and tasty variations while increasing the nutrient value. If you can eat legumes, add a tblsp soya flour.
Fruit loaf:
With or without these, add dried fruit or chopped tinned fruit, a spice or two (cinnamon, nutmeg, ginger, small amount cloves, cardamon, coriander, vanilla, almond essence) and a tblesp raw sugar or similar. If you can eat barley, you can make this into malt loaf with a tblesp malt. Tuck a piece of dark chocolate into a bun before baking for pain au chocolat, or marzipan for stollen.
© Anne Wade