Hi Hawkssr,
I'm sorry about your weight loss! I'm also 77 and have a weight loss problem. However, mine is due to incontinence. Your problem sounds really difficult. Perhaps you should quit walking every day. Many people who weigh too much often sit on the couch and watch TV or get on the computer a lot. As far as an inexpensive diet to gain weight I would suggest making beans from scratch. Buy some white beans or any kind you like. Soak them overnight and then rinse them and cook them in water until they are done. They are great with butter and salt and pepper or you can add tomato sauce, brown sugar, onions etc. You can find the recipes on Betty Crocker at https://www.bettycrocker.com/ Beans are a great source of protein and high in calories. Also make split pea soup from scratch. You can get that recipe from Betty Crocker too. Split peas are very cheap as are beans. Split peas are also a good source of potassium and high in calories. Keep in mind you can make split pea soup without adding ham as most recipes suggest. Corn and peas have a lot of calories too. Have you tried looking up a calorie counter online and eating only the highest calorie count foods that are inexpensive? Noodle dishes are also high in calories such as macaroni and cheese and spaghetti. Make your own. Don't buy the mixes. They are full of junk that won't help your problem.
Good luck!
PML