A Soyuz booster can put some pretty sizeable payloads into LEO for about $1000 per pound. It's even man rated. Unfortunately, it's built "elsewhere". The Soyuz booster comes pretty close to the alternative idea called "Big Dumb Boosters" in that a relatively simple, produceable, and proven design gets built and launched in large numbers, lowering the costs considerably. Counting the Molynia variant, about 2000 of the Soyuz/Molynia boosters have been launched with a very good reliability rate (and 0% reusability). It's a damned fine booster.

Strictly speaking, we don't need CATS to go to Mars although it would make repeated flights more economical. If the cost of developing CATS gets rolled into the cost of going to Mars (and those opposed to Mars missions would certainly try to do this), then the cost will be much higher.

CATS is a good idea, but don't look for it to come from NASA, Lockheed-Martin, or Boeing. They have no incentive in lowering launch costs. While Beal broke my heart, look for alternate companies to do the work if you ever hope to see substancial reductions in launch costs. Fortunately, at least one company is close to making it happen. The first flight of the Falcon I light booster is set for this summer. Their bigger Falcon V is projected to be able to launch up to 4200 KG into LEO for $12 million ($1300 a pound). Let's hope they succeed. If they do, it'll put real price pressure on LM/Boeing for the first time.