Cheap access to space - again (was: Audacious Tactics)

The CAIB report has some details on shuttle turn-around time
and extent of rebuilding. I was quite surprised - a lot of the
external tiles and frame of Columbia were "original equipment" -
it's mainly the engines that have to be rebuilt every time,
although I heard elsewhere the longest turnaround time had
something to do with loading and unloading payload...
Maximum launch rate (pre-Challenger) was 9 in one year, with
4 orbiters; if I got the right numbers from the CAIB report it's not
the rebuilding of the shuttle (which takes just over 2 monthns)
that is the main barrier to launching more often.