Enter a 2v2 Multiplayer game with a friend on the same team. Set the other team with two AIs on Heroic or Legendary; it doesn't matter which. When the game starts, have your friend exit to the Xbox Dashboard. The game will automatically end, declaring you the winner and unlocking the achievement.
Enter a 1v1 deathmatch game against the AI on Heroic. Use the Prophet of Regret and the AI as the Brute Commander or the Arbiter. Right when you can, create the Temple and the factory. Create five or six Locusts and send them and the Prophet through the teleporter. Head straight for the citadel and destroy any building the enemy is constructing. Do this right and you can get the Penny Pincher achievement.
Enter a 1v1 regular skirmish game (Heroic) on Chasms, the player as the Brute Chieftain or Prophet of Regret (all you need is a very basic rush strategy) and the enemy as Captain Cutter or Sergeant Forge. Build a temple first and then a supply pad, scout for crates and then send the leader (as soon as possible) to the enemies base to start harassing new structures being built. Set your bases waypoint to the teleporter so new special infantry units teleport to the leader upon being trained, use all remaining starting resources to queue up brutes or elite honor guard then build another supply pad and continue training more of these units. Using brutes or elite honor guard you can destroy the enemy base, done correctly both this achievement and Penny Pincher can be unlocked simultaneously.