I haven't been paying close attention to the Ares heavy lift designs. Are folks still debating SSME vs. RS-68?
I imagine the SSME is vastly more expensive, although more efficient:
SSME --- 3.2 mega Newtons, 485 sec. Isp
RS-68 --- 3.3 mega Newtons, 420 sec.
So they're talking about putting four or five engines like this on a first stage.
Just to point out, if you reverse Tsiolkovsky's equation, the mass of fuel you need is an exponential function of specific impulse, so there is a real reason the Russians went crazy getting close-cycle engines to work. And these modern engines are hugely superior to the F-1, both because of LH2 and because of better design.