What’s the cheapest way to gain weight?

Always wondered what the cheapest way to gain weight was IE good fast food deals, cheap gainer shakes, snacks, and everything of that sort. I’m a 19 year old male who’s around 250 and would definitely be immobile if I had the funds so just figured I’d ask. My gains have been mostly from eating whatever I want whenever I want but I definitely gotta be smarter about this. this parts just filler to make it long enough to post.