This is not my work - got the information off of another site I frequent that posts tips for obtaining trophies.
This is essentially the amount of money that needs to be earned in the missions to get gold and get Xp. The vast majority of points are awarded for kill streaks - so kill streaks should be a major focus in the missions. Also it states not to leave behind enemies (like on that river mission Jay... where we left that one guy)
Advanced Co-Op Missions:
Points vary on group #
For Gold
Group of four - 10,000 points ( people have reported the herd with 7,000 points) Aim for 10K though to be safe
Group of three - 7,500-8200 Not sure but between those
Group of two - < 6,000
The Herd: Group of four (7,700 < 8,000 (15 cows herded) reported see post # 7
River: Group of two 9,000 scored 24 minutes.
The Herd: Group of four 5,700
River: Group of four 8,680 (Silver)
Group of four: All missions
The Escape: $ 8860
Ammunition: $ 8750
The Herd: $ 6040
Kidnapped Girl: $ 8045
Walton Gold: $ 8640
I suggest all being leveled up and choosing the all weapons class (no holds barred?)
On most maps especially Ammunition, Escape,kidnapped girl use the sniper rifle and only shoot when guaranteed a head shot. Doing this enables a 2x multiplier and can generate from 25-125 per kill depending on kill streak number. This also adds up money for getting kill streaks.
Escape: group of three- Always have someone ride as a horseback. At initial start have a lone sniper rack up the kills ( can get 1400-1700) Use the cannon at tumble weed and have someone play medic to cannon, and the other watch flank with dynamite. *NOTE* you can sneak attack cannon area by climbing the mountain to left of yellow pathway marker (near gorge) On escape wait for guys to ambush and send ahead a scout to engage enemy.
Kidnapped: Group of two - (let a sole player kill the opening guards (10-14) and for additional $35 let them remount the turret. *Watch out for the guy on top right of hideout* If the player does this correctly you can easily net 1600-2400 off the start. Once you gain the girl and start the escape always stop for enemy ambushes and have one player ride on horseback (enemies tend to go for wagons if the horse rider strays) Nearing the bridge stop and both get out and start sniping *head shots* Can get 400-600. Nearing the farm stop before the enemies notice, exit and circle the farm attempting to get head shots.
Walton's Gold: Group of three - ( Have two stay at the start and snipe heads only) The other does a master flank flanking the top turret guy and the sniper, ending up behind all remaining enemies. Grab all the hold (not sure the bonus obtained, however there is one.) On the ambush remain in the house until the group clears a solid side of the map and start to move around.
Ammunition: Group of three - On the start have two players throw dynamite in each entrance point and have the other rush the right entry way. Upon clearing the fort re group and push out the left entry (from spawn) and push into the left rocks (going Rambo with Mauser pistols on hostels in rocks. Have one player watch the back turret gun and keep them occupied while one of the remaining players snipes all enemies on sandbags (12-14) 1400+. If he runs short on ammo kill the rest off and push toward Hill once safe partially up hill have player three snipe turret enemies and enemies near hill top. Once you gain the hill simply wait and look towards right entrance of fort and provide fire to the enemies to the west.
River: Group of four (vote bottom person out before getting to final point. Play the map straight up and upon departure from the second shore point team total should be around $4,000-$5,000. Upon arrival to final spot have one player (worst) stay on the dock and play medic. I suggest clearing the left side and yellow dots first, however anything works. I've encountered a infinite spawn glitch, were the enemies continue to spawn unless the medic player moves forward on the map. This is both great and dangerous, anyhow once wrapping up the enemies if short have medic player get voted out.
The Herd: Group of three- Have one player continually snipe from the start attempting to get head shots, have others play medic until their ammo runs dry and switch. *NOTE* Can get 10 kill streak reward at start* After finishing off the enemies, have two players scout ahead and engage the spawning of the enemies while the best herder heards the herd. You can get gold with a minimum of 6 cows and 7700 points.
Other tips:
-Always refill your ammo, the sniper can make getting gold a breeze.
-If short on points vote out person in last (Be mutual about it if working in a group)
-Dynamite is your friend
Always stop on wagon missions to kill approaching ambushes.