Don't put them together. If you can't afford cages for each one, you can't afford that many snakes. There are various reasons why you shouldn’t house snakes together. There are even more reasons if they aren't even the same species. A few reasons being....
B) Care requirements
C) They aren't social animals
D) The spread of bacteria or mites and ticks and etc
There are more reasons, but I just wanted to list a few for you.
When it boils down to it, if you want 3 snakes, buy 3 cages.