If you are happy with the way you are - then just rise above it. Best option is to take the piss out of them back for their over the top food choices. Show them that you can take a bit of banter, but you will give it back too.
If your not happy with the way you are - then there are ways of eating very good food, very cheaply. As a student I used to live on a tiny budget, but would cook food that was hardly distinguishable from the students with much bigger budgets. You just have to think cleverly, look for good value discounts, shop at the end of the day/week, when discounts are cheapest - try markets instead of supermarkets for some late-day great deals on fruit+vedge. Buy ingredients that last a long time, and ration them out, and cook fresh for the most part, but only using the cheaper vedgetables. There are a lot of ways you can make potatos and onions taste great, and they are dirt cheap and last for ages.. forget the aubergines and the organic whatever though..
If you dont want to do any of that - thats ok, its a lot of effort, and most people just dont care. So just grow a thick skin, give back as good as you get, and show them that you do what you want, and do not cave to what others think. In the long run they will respect you for that, even if they dont like it/you/understand.