Hello--
The species you are keeping have different temperature and humidity requirements, especially during the colder months. As such, there is no one answer to your question.
The ball and the blood require a constant warmer heat gradient year-round. The corns and kingsnake require cooler temps, especially if you are cooling them/brumating in hopes of breeding next season.
Suggestions:
First, decide where you are going to have them--all in the same room or different rooms? Make sure that there are no cold drafts which can cause temps to fluctuate. Are there windows in the room which will give the N. American colubrids seasonal cues in terms of light? Nature may tell them to brumate, and stop eating--do you want this?
Second, find out the heat requirements for each species, and provide two thermometers per enclosure--one for the warm side, and one for the cooler side.
You will probably have to experiment with heat/basking lamps and UTH units to provide the proper heat gradient for each snake. The energy cost of heating 4 enclosures should not be that great. Your cost will be in heating fixtures should you need to buy them.(Try your local Home Depot for clip on lamps and bulbs--much less expensive than the pet store equivalent.) The UTH are pet store items. Yet, when compared to the cost of taking a sick reptile to the vet, the heating fixtures are a deal; especially when the vet will tell you that the first thing to do is provide proper heat for a sick animal.
Best of luck!
althea