Rounding up actual human beings and imprisoning them cost so much more than just leaving them be. Despite the rhetoric, most immigrants pay taxes without getting any of the benefits of doing so. This was never about that.
Trump's major donors were the For Profit Prison System. Are they all racist, yeah, probably, but it's more than that. They don't care who they put in there, it will be anyone they can get away with.
These people have been turning America into the world's largest pyramid scheme, now with prisons for anyone who questions it.