With a Algea Scrubber, you can get away without a skimmer, and it doesnt require any more water chjanges then you would need with a skimmer, but a algea scrubber costs alot less then a skimmer. Nitrates/Nitrites/Ammonia/Phosphates all should stay 0 when setup correctly. But at the same time its not a bad idea to have a good skimmer in a pred tank, as preds make a little more mess, though with enough biofiltration a scrubber would be ok, even with a messy pred.
But at the same time if you are that concerned about the money then maybe salt isnt for you, its a beautiful yet costly hobby, and failures in salt result in hundreds of dollars to thousands in losses. And maintinance isnt exactly free eather.