Have someone dress up as an old lady, or just go find one. Go to a funeral home telling the person working that you need to plan your grandma's funeral for next Saturday. Be sure to introduce the old lady as your grandma. Tell him you get a good inheritance from your grandma so you don't have to worry about the money, also tell him you want to buy cheap because you would like to get a new car, a pool, a new house etc. When they ask why you are planning the funeral so soon and your grandma seems perfectly fine, just be like I know what I'm doing. The whole time your "grandma" needs to be shaking her head and whispering for help.
Have an iPhone? Check out all 200+ new features coming in iOS 13.