Hello! I am a fellow victim follower of the FODMAP diet.
Firstly It absolutely IS boring, restrictive and demoralising at first, BUT remember the things you CAN eat. So ALL meat and fish are fine, Rice, Potatoes and Polenta are good.
Someone up-thread said lentils, but they are on the red 'no' list in my fodmap guide.
I think the herb you're talking about is Asafoetida, It's actually a very good substitute, but you need to be not too heavy handed. I used smoked paprika, and asafoetida in place of onions and garlic which were the ingredients I used to start EVERY dish with.
I'm afraid you are going to have to learn to cook from scratch a bit more. That's what I had to do too.
I suggest you learn how to make Spanish omelettes, and also Risotto. you can then add veggies and chicken or fish etc to the risotto and it will give you some variation on a theme for your tea. plus will be tasty enough that the rest of the family can eat it too. Also there is a variety of 'freezer food' which is suitable. For Example Sainsburys do frozen quarter pounder burgers which (unlike many others) don't have onion in them. Chips also ARe still do-able in the oven even without oil, and you can do sweet potato ones too.
The lack of stock powders/cubes/pots that are suitable is the hardest thing to replace in my experience. I agree that a lot of things are out of budget, I am on a limited income too, but I would suggest that the 1 thing which IS worth it and not too much more expensive it GF pasta, Sainsburys own is good.
Try not to lose too much hope OP and speak to your Dietician, you are supposed to be able to trial the different segments of the FODMAP diet to work out which types of sugars are actually affecting you specifically and so some things may come off your list for you eventually.
If you would like any particular examples of meals then PM me and I'll get back to you with whatever answers you need.