The under tank heaters are definitely better than lights for ball pythons (or so I hear haha) because they need "belly heat" to aid in digestion. Also, the Acurite thermometer/hygrometer is only $12 at WalMart, making it a far better deal than the stick on thermometers (you know, since they actually work)
you also do need something to control your heat source, but that can be as simple as a "lamp dimmer" (found in the lighting section of a hardware store or some WalMarts as well. Just a dimmer switch that you plug into the wall and then has an outlet that you plug your UTH/lamp into)