mountain bike wanted

[taylor p.]

my dad is looking to start doing someriding with me and so he would like to up grade. he would like a good bike around 500$ with a frame size of 20-21.
thanks

[FarmerBEN]

you could probably find a new marlin or Rockhopper (I think for that range) both are seem to be solid frames with good enough components to start with, and a frame worth upgrading as you replaces stuff.