John,
Most of the US Army CH-47Fs will be new builds, or modified late production Ds. The cost delta between new and refurbished (particularly for the older airframes) was quite small in the end. The Chinook also doesn't suffer from tail rotor vices/compromises, is largely impervious to wind, is much smaller (it's relative...), can be flown more aggressively in the latter stages of a zero speed landing and is substantially cheaper to buy, fly and operate with an extensive worldwide support network, rather than relying on one customer with a limited fleet. The proposed Block II -47F will close the gap somewhat in terms of lift as well. The -53K seems to be exactly the aircraft the USMC wanted, and I agree it's in a different class. It seems like an awesome piece of kit if your mission set really needs it or you need to spend a prolonged time embarked. If not, buy the -47F and spend the (considerable) change on avionic/DAS upgrades and flying hours.....