You got in the game way late.
5.45 is really slim to none lately and for the foreseeable future. Sure some folks will dump it at shows and occasionally online, but I used to be able to get a spam can for $129/1080 rds.
But I did find Wolf 55 grn. 750 rounds at ammosupplywarehouse.com for $197 including shipping.
Considerably more than the $129/1080 but it won't be my primary.