I bought two idler pulleys from Autozone for my 2000 base Boxster. The new pulleys are an exact match for the top idler and comes with a new short spacer for behind the pulley and has a new front washer. Removing that long bolt was a PITA.
The lower idler is the identical pulley compared to the top one but uses a longer spacer behind the pulley so I just re-used the old one.
The price was about $46 for each so they are relatively inexpensive.