do you want someone to just tell you how to make gil or something?
1 solo character can make 8mil per gain with trusts. 10+ per gain if you team up with people and have a good camp. Not botting.
1 solo char as mentioned can make 20mil/week in omen, again with trusts no botting.
you can make at least 50mil/month on sellables via ambuscade points. Oh my, no botting!
do one cycle of a HTBF on VD with friends once a week (8 kills, the KI you store plus spending 70 of your 75 stored merits, then quickly cap merits at gain) will net you likely another 5-8 mil depending on values of what you get.
so using the lowest numbers I listed, and only make 1 gain per week (assuming you have commitments or scheduling issues that would mean you can't make more):
4 gains per month @8mil each= 32 mil
20mil per week in omen= 80 mil
50 mil per month from ambu = 50mil
5 mil per HTBF cycle per week=20 mil
182 million from 4 sources per month. More than enough to buy that Rostam and probably half of the upgrade mats.
And if you're gonna complain that a weapon of the value that a Rostam has isn't worth a month, you're going to get zero sympathy here. Most people around here who have multiple RMEAs got their first when it took 8+ months worth of work to get the level 75 version.
As for upgrading, dude just equip it and kill stuff in dyna-D with a shell. Won't spend a dime. Or use the drops you get in that dyna-D run and double dip your upgrade speed.