Uhhhh MC, you need to buy a freaking anti-aircraft tank for this level of a fight, don't you? A Gundam, perhaps?
Joking aside, I get that he doesn't have enough CP to buy more stuff & everything's freaking expensive. He's doing this kinda missions too early for his inexperience too & he should've gone for smaller missions to collect more CP & gather more info about the places he'd go in the future. What he severely lacks might be his own undoing, but it's also his strength, as he isn't afraid to go forward in his new life in an unfamiliar world. He's unpredictable.