I don't understand why you think this is a more expensive diet, you don't need special weird foods. The main things you have to cut out on low-Fodmap are garlic, onions, wheat, rye, milk (but not cheese and butter), beans and peas and some sweet fruit / veg. You can eat meat and fish, eggs, butter, cheese, potatoes, TONS of veg and fruit, corn, tofu, rice of all kinds (inc noodles), polenta, quinoa ...
Many 'ready made' foods are out because they contain onion and garlic powder and other cr@p but although I work long hours and don't cook elaborate food at all, I've never had a problem making meals. My blender and microwave are my friends and there are low-Fodmap herbs and spices which can flavour most things including hing (asafoetida) which is instead of onion and garlic.
The only 'different' things I buy are substitute breads and crackers which are usually made with rice or corn flours and the ones I buy aren't expensive, but you could make your own rice bread, and lactose-free milk (for calcium and vitamins, I wouldn't buy 'almond' milk, there are almost no almonds in it, take a look at the list of ingredients), which is about half as much again than own brand ordinary milk in my supermarket.
I've been on it for 2 years, don't even think about it now, and have benefited so much: no more pain or bloating and I've also lost weight.