It's really going to depend what is on the rifles you are looking at.
Rails or no rails, sights or no sights, chromed or non chromed bolt carrier group, removable carry handle or no carry handle, Gas port with rail or no rail, two stage trigger or single stage, 4 position or 6 position stock or A2 stock, commercial parts or Mil-Spec parts, 5.56 chamber or 223 chamber, flash suppressor or muzzle brake?
Each one of these parts costs extra if purchased seperately. Comparing one AR to another is not as easy as it may seem.
Do more research on them first and then ask again with more information.