In many ways, a lot of local cuisine is inspired by financial necessity - after all, the local speciality is usually something very available in the area, and so cheap because of supply and demand.

I'm researching the Victorians atm, and these books tell me that stews, casseroles and soups were extremely common at the time because meat was very expensive, so most people who could afford meat could only afford small amounts and not the best cuts. These dishes make tough cuts of meat palatable and can be bulked out with cheaper ingredients, and many of the dishes popular at the time are still enjoyed today: Irish stew, Lancashire hotpot, and the classic British beef stew with suet dumplings.

Potatoes also became much more widely eaten in the Victorian era due to the Corn Laws, which made bread much more expensive, and also because potatoes were a cheap crop to produce, providing plenty of storable food and growing in poor soil. We still use a lot of Victorian potato recipes, and they are often linked to the regional cuisine of the areas that were most impoverished - and thus, needed to rely on potatoes - at the time. This is especially true of recipes that substitute potatoes for a more expensive ingredient, such as Scottish potato scones, Lancashire butter pie, boxty, potato bread.

These are just some examples, and the ones I have references for. I've certainly heard of a lot of other dishes that they developed from economic necessity; cajun cuisine is something I hear this about a lot. But I don't have references for that.

During the depression, the government issued large numbers of cookbooks which used little-known and less costly ingredients. Many of these were to be cooked in a casserole type dish/pan. These were highly influential books, and definitely increased the "popularity" of casseroles. So, I can't say that the cheapness was the only reason for the interest in casseroles during the depression, but that was a major reason, along with the government-issued cookbooks.