I bought a cheap Hovabator to try hatching eggs, and wasn't happy with how much the temperature fluctuated It seemed I was always fighting with it to maintain stable temps and after opening it (which I tend to do a lot) it took too long to come back up to temp. I ordered a fan for it (still waiting for that to arrive) but for this hatch I put a 7W reptile pad in the bottom, where the water tray usually goes. This little radiant heat pad runs 24/7, and while it isn't enough to keep the incubator at temp, the ring style heat element the bator came with doesn't click on and off as often. This has created a more stable constant temperature, and after opening it comes back up to temperature quickly. It seems to have really reduced hot and cold spots too as the entire pad heats up, creating a bigger warm zone than just a small metal element does.
You can buy low wattage heat pads fairly cheaply at pet stores. Just thought I would pass it along to anyone else with a cheap incubator.