An el cheapo thermometer is fine for checking temps of roasts and chicken, but it takes some experience and skill to get to the right temps effectively without exceeding them and ruining the meat. Sous vide is a different league, it allows you to accurately reach the right temps on delicate and expensive proteins where 5* off is the difference between perfect and $15 a pound garbage. They're not really used interchangeably, they have different roles. $20 for a sous vide circulator is a steal, if you like good food, grab one and learn to use it.
That being said, it shows as $79 for me too.