This is best done solo but it does work well in coop too. Using this method I had no trouble doing it either way.
Routes
Round 1 - Money
Round 2 - Supplies (Turret)
Round 3 - Money
Round 4 - Weapons (Grenade Launcher)
Round 5 - Money
Round 6 - Supplies (Mine)
Round 7 - Health
Round 8 - Weapons (Shocker)
Round 9 - Health