My cheap ready made items are Gatorade powder, dried apricots or a banana, and Nature Valley crunchy granola bars from Sam's Club. For general training and riding, the name of the game is carbs that digest easy, and don't get messy / inedible when hot. That's the problem I had with trying to do things like rice cakes and other kinds of homemade energy bars (heat).
I also have a giant tub of maltodextrin to make DIY drink mix, but I didn't get it right this year, with a couple spectacular blowups from too much maltodextrin (which is usually very easy to digest) basically becoming a bomb that shut down my stomach. Next year I will experiment more with using stevia to add a slight sweetness instead of sugar in a lower concentration, and also using those coil things in my bottles to help it mix better. There's nothing wrong with Gatorade, but for very long rides it does get a little too sweet, and it isn't good for your teeth.