They can be set up with DIY degree circles for cheap/easy navigation (scope is useless if you can't find stuff with it).
For $500, I would look at a 5" or 6" F5 reflector.  5" scopes like the AWB OneSky/Heritage 130 or Zhumell 130 on a minidob mount provide good all around performance in a compact package that is easy to transport and setup.  They are a compromise between wide field viewing and high magnification viewing (Most scopes do one or the other and are therefore more specialized).  They can be set up with DIY degree circles for cheap/easy navigation (scope is useless if you can't find stuff with it).  They generally sell for around $250.  This leaves money in the budget to get a barlow and an eyepiece or two (Most scopes include a low power and mid power eyepiece of reasonable quality, but nothing for high power), a UHC filter for nebula, and a variable polarizer filter to cut glare on the moon and planets.