Here is my strategy for the Mercenary map:
1) Power on and unlock door by suppressor 1
2) Purchase turret in suppressor 1 room
3) Activate suppressor 1
4) Open main gate near Suppressor 1
5) Bring turret with you, power on and unlock door guarding suppressor 2
6) Activate suppressor 2
That's as far as I've gotten on this map, but it seems to be the best strategy so far. A lot of the paths at the start are dead ends and wastes with nothing but ammo and health in them.
For the Tribute map:
1) Go through back door entrance for $2500.
2) Buy Turret and activate Suppressor inside.
3) Go upstairs, jump out the window, grab turret two from the locked shed and activate Suppressor 2 below.
4) Save up by the health and ammo cache until you can blow up the metal gate for $8000.
5) Activate the third suppressor outside.
6) Go back upstairs to where you jumped out the window originally and hack the door for $7000.
7) Grab the third turret and activate suppressor #3.
That's as far as I get. Usually that third suppressor Alien wave kills us.
General Tips
-- Don't waste your money on a buy-in unless everyone on your team is dead and a game over is counting down. Even then, you probably only want one player to buy back in to conserve the group's funds. If your buddy can complete a wave on his own, all the dead players will respawn with full ammo without having to buy back in.
-- If you're out of ammo and the wave is almost over, it's cheaper to just kill yourself and respawn next wave with full ammo than to pay $750 to refill your ammo.
-- Turrets are beastly. Get them ASAP on every map because they are portable and you can refill their ammo for only $250 when they run out. You get $75 for each turret kill.
-- Smartguns are also a great investment since they come with 600 rounds. Buy one if you see one.
-- Use your pistol as much as possible to conserve ammo.
Added my tribute strategy.
