Hi. For me, low fibre options are best. Relatively cheap foods that are easy on my digestion include white rice, white bread, peanut butter (good if you need to gain weight), low-fibre breakfast cereals like cornflakes or rice krispies, and bananas.
Limiting your diet may not be the best thing long term, but if you're going through a bad flare it might be worth limiting your diet for a while.
I've tried a diet of all organic food, and tried giving up dairy and gluten, etc. None of these things helped me at all, so even though the cost issue prevents you from trying some diets, they wouldn't necessarily help you anyway. That said, I think gluten or dairy free diets can be done without adding too much cost, though I don't think you could do a organic diet without spending quite a bit more.
And there are things that are generally not good for you which, by avoiding, you may be able to reduce the cost of your food if you're not avoiding them already. Alcohol would be the most obvious thing here. And by not eating out or ordering takeaways you can save some expenses. Again, you may do this already but I thought I'd mention it just in case.
Of course it may be that you're going to feel bad at the moment no matter what you eat. Some times it's not the kind of food that matters - just eating sets off symptoms. If you're struggling with eating to the point of losing weight, it may be that you need to get checked out to see if your Crohn's is getting worse of if you've developed a complication, and perhaps you need a change in medication or something else unrelated to diet in order to make eating easier.