That will probably be Match quality ammo. Expect to pay around $15-$25/50 rounds. Rounds I have used with good results are Lapua Master, Nobel R-50, Fiocchi Match, Eley Tenex. Wolf Match is also very good. Disappointed in Winchester Match.
HOWEVER- unless you are a SERIOUS competitive shooter, you will not see a major difference between GOOD ammo and EXCELLENT ammo. For GOOD ammo- and a lot less money- Federal Champion Target, and CCI