I was vegetarian for about 15 years, and vegan on and off for parts of that. I say "was", because since moving in with my omni boyfriend, there has definitely been some cross contamination going on (i.e., if we are having eggs for breakfast on the weekend and he wants to fry his eggs in leftover bacon grease, I can't be bothered getting a second pan dirty, so my eggs get fried in the grease as well), and I also do eat meat with him on occasion (maybe 1-2x/month). I don't eat a load of dairy or eggs, so it's quite common for me to have days on end of vegan-only eating. Since moving in together, the boyfriend also eats a lot less meat, because I do most of the cooking and there's only so often I will cook it for him :) Plus, we both agree that if we're going to eat meat, we want it to be as sustainably raised as possible, and that kind of meat is EXPENSIVE! So I don't really see it ever becoming a huge part of our diet.
My reasons for shifting to a more plant-based diet were pretty much entirely environmental. I was too young to really be concerned about health benefits (what teenager cares about their cholesterol or blood pressure?), and while I'm aware in the abstract that farmed animals don't have the happiest lives, I guess I'm not quite empathetic enough to change my diet for them (sorry, hope that doesn't make me sound totally heartless). I'm still pretty concerned about the environmental costs of eating meat, though I'd say health and budget benefits definitely contribute now too.
While we do buy some produce organic, we're not fanatical about *everything* needing to be organic, so I would say our diet definitely keeps our food costs down. There are a few things I will only buy organic (like strawberries), for those things I wait until they're in season, pig out then, and take a pass for the rest of the year. One thing that has made my diet more expensive in the past couple of years is eliminating most soy from my diet (I cut it out in an effort to reduce my super heavy periods, and it worked, so...). To keep my protein intake up, I have wound up supplementing a bit with protein powders (rice, pea, hemp), which are more expensive than, say, whole rice and beans. The cost per gram of protein is still much less than for organic chicken, as I remind the BF whenever a shipment of powder arrives and he asks how much it cost! I've tried to get the same amount of protein from 100% whole foods but I find I do just feel a lot better when I'm getting a more concentrated dose each morning, even if using protein powder does feel a bit wasteful or frankenfood-y. I did actually have some bloodwork come back a few years ago suggesting that I was not eating enough protein (one of those things the intro vegetarian nutrition literature always tells you is impossible), so I do try to keep a closer eye on it now.