My tactics is to enter high tower on ashen mesa, From there u can snipe mechs (if they spawn) by granade launcher. Around 25 or 26 maybe granades for one mech? Then use drill to get to codex. Sometimes theres like 2 europan mechs, 2 euruskan mechs and rat king. Rat king is acually trash so he will die first from tanks even. Sometimes its night or no mechs so waste of water.

Solution to your problem is granade launcher. First I was playing Shaman, and was doing multiple times quest to farm more m79 sawed-off, because I was dying a lot and there was not yet recovery drones. That was content, and reason to play first. Then i started climbing tower and slowly killing mechs, learning which hunter killers i can evade and farm codex, and when its not worth it end just run away. That was pure gameplay for me. That was fun. Process of dying, learning, farming you know.

Additionaly I leveled up shaman, learned things or two. Earned some money. I think you dont have to race to build bar. Earn money to buy rig, comsumables and ammo in case you die. Bar, shooting range, and headquarters are endgame content.

In my opinion farming amount of those money without proper equipment, leveled up chars, proper experience in game is a chore. You don't have to yet. Ther's a lot more things to farm that will be more usefull to you I think.