I'm sorry to hear of your struggle with this.

After much trying out with different diets I've now come to the conclusion that the only way I can be pain and a few other not nice things free is to follow a gluten and dairy free diet. The Drs say I'm intolerant, so I know it's not quite like being allergic. It sucks, and is difficult to follow especially if like you said when eating out. I don't always follow it, and can get away with it taking various pills. The only thing I tend to find if I'm on it is chips, and I have to make sure they've not used any additives to make them. The other option would be a plain baked potato, which I guess you could add butter to? I know that's not very exciting though, and doesn't solve the problem.

The more and more you get used to being creative with food and finding things you like, the more likely you'll be able to cut costs. I rarely use the gluten/dairy free specialist products, which does cut costs too. But if you want to use them, you may be able to buy in bulk online or just online for cheaper. Also, try new things, like different pulses and vegetables you've not tried before and look online for recipes, these foods are quite cheap and good for you.

I hope something in that has been of help!