CH, you're going to have even less money if you keep trying to incubate eggs with a faulty thermometer, and you need a hygrometer to track the humidity. Without those two items, you're fighting an uphill battle that's all but impossible to win.
I doubt if there's anything wrong with the incubator you have, except that screwed up thermometer. Plenty of folks have had successful hatches with the same incubator you've got. Is it the best?..NO. Can you afford to replace it with a better one? Evidentally NOT. So you make the best of what you've got to work with right now. Unfortunately, you don't really have anything to work with until you replace that faulty thermometer/hygrometer. That's just the way it is.