There are quite a few brushed motors in the $20-$30 range that are supposed to be very good and rebuildable.
Brushed motors seemed to work very well for rock crawlers.
For the average Joe a brushless motor will work better than a brushed.
But from my own experience and from numerous threads around the interwebs the brushed motors that come with most RTRs are complete crap and you have to gear down the vehicles so that the motors do not overheat, just do a Google search on the Titan 550 12T. The brushless systems are hands down a night and day difference.