Hey don't be so harsh on yourself! The point is you want to fix the problem. I would get the hydrofarm because a 5 degree swing is better than a snake sitting at 140 degrees F. If you do buy a hydrofarm I would buy a temp gun as well to double check the temps. I have a VE 300 and I have a temp gun too. I've heard of MANY people using hydrofarms and their snakes are fine. I think everyone here will agree that a hydrofarm is better than nothing.
Also you have to do this TODAY. You have to get a thermostat today. This is pretty much an urgent situation and your snake will get very very I'll. they come from tropical Savannas located in Africa and its quite warm there. They've adapted to living in that temperature and they will surely get sick. Good luck