If you only have $70, you are looking at dimmer switches or an on off system which really are not the best... herpstats are the better one but your are looking to spend at least $135 on one of those. If you do not mind an on/off system, you could try the stc 1000. It is roughly $28 on amazon... but I have used this thermostat. Basically you set it to a specific temperature in celcius. Then it heats the heat tape to full power until it reaches that specific temp then it cuts ALL power to the heat tape. When the heat tapegoes down a couple of degrees, again the thermostat will turn the heat tape to full power. Not very good in my opinion, especially since heat tape can reach 120F on full power. I am not sure how it would work in an incubator though... I used it in a snake rack and eventually I paid the price by it burning one of my snakes. A dimmer switch would be the next best option as it only allows a certain amount of power flow through the heat tape, but it fluctuates depending on the temperature of the room. Also not a very good idea for an incubator as well. I seriously think if you are talking about eggs, you need something a little more professional otherwise you just might run into problems during the incubation with means dead eggs, deformed and undeveloped babies. But that is just my $0.02. Good luck!