"5 series" is somewhat of a mixed bag for Trek and has different kind of bikes models, which, to add to complexity vary from year to year both on frame composition and component level.
520 are touring bikes
560 (and 560EX) are racing bikes and at some point were the top of the line Trek racing bikes with 600 components, while at another point there were mid-entry
510 was a "sports" bike that yet for a couple of years came with Campy components (Victory or Triumph, cannot remember)
So really, year and model (or a picture) are fairly important to answer this, but I would agree $5xx is too much