Constantine might fare better on a network like Fox or even FX, HBO, etc. If one of the cable channels picks it up or even like Netflix, they could push the envelope a little more. Having Zatanna appear on Flash, Arrow, etc would be awesome since she is part of the Justice League. And, she had a relationship with Constantine.
The expense is in part due to the special effects they have to generate per episode. Plus, rigging for stunts. Those can run up a hefty bill, but I think if DC/CW plays it right can work in their advantage. The tv shows have been really what has been a lifeline for them. Even the animated tv shows and movies. The effects for the shows are on par with the movies. Light years ahead of where special effects were ten even fifteen years ago. Half the time I forget I'm watching a tv show.