Re: Don't call it "re-used"
The shuttle had unanticipated costs. The entire vehicle had to be refurbished, which included removing the engines and shipping them to a separate facility to be completely rebuilt.
A great deal of the cost was in replacing the heatshield tiling, which was an extremely time consuming process. It had been originally planned that the shield would be made from generic tiles over most of its surface, but they ended up having to construct custom-shaped files for nearly the entire shield, which massively inflated the costs there as well.