Gluten is often in sauces, gravy, soup, cereal, sausages, burgers, some crisps, biscuits, crackers, etc
Yes, and it's also in lots of places you wouldn't necessarily expect to find it. When DD was first diagnosed it was a massive learning curve, it had never occurred to me that vinegar, hot chocolate, simple stuff like that was a no-no
I do cook everything from scratch (including bread, cakes, etc), but in my cupboard I have a box of cocoa powder which "may contain traces of gluten", and various other bits and bobs with the same disclaimer.
Things like GF suet is more expensive, when the only difference is the use of corn flour rather than normal wheat flour.
DD does get a free prescription for bread (we don't use it), but she's 13, other adult coeliacs I know have to pay the normal prescription price