I was told the "hot ticket" for newbies for NRA Service Rifle was a Rock River lower with their match trigger mated with a White Oak Armament upper. WOA will also do a trigger job on your RRA trigger.
If you are going to be at all serious about trying Highpower, more then just a single match or two that is, you really do need to invest in a good quality set up.
I was told the RRA/WOA combo would be good enough until you wore out the barrel and needed to replace it anywhy, and at that time to upgrade.