Let's slam through the basics.
Fixed costs: docwagon (assume gold, because sooner or later you're going to pay HTRs and docwagon survivor fees), maintenance of gear and supplies, and lifestyle expenses. Assuming middle lifestyle, you're looking at a fixed cost of between 8 and 10 thousand a month.
Variable expenses: you're going to have expenditures such as ammo and repair/replacement of gear. While each mission will vary I'll assume a floor of 2,000¥. Yes, some runners can do it for less than a thousand. I am not sure how they're repairing armor and clothes, but that's the claim. Thing is if the mission goes pear-shaped the costs will go higher. If you're not getting "expenses" you need to get enough from the inexpensive runs to pay for the expensive ones. If you assume a nasty run forces you to dump 10% of your gear that's a nominal 25,000¥ (10% of 50 BP chargen cap for gear @ 5000¥ per BP).
Swagging that last paragraph, assume 4 easy and 1 ugly. 8,000 + 25,000 is 33,000, divided by 5 is 6,600¥ breakeven variable expenses.
Assume, for easy math, ten runs per year. That's 66,000 for variable expenses and call it 100,000¥ for fixed for 166,000¥ per year. That means your runs should be earning you an average of 16,600¥ for pure breakeven. Note that paydata and fenced goods can make up for part of this.
If you do 25 runs a year, or just over two runs a month average (easy runs don't force you to hide so you can do them back to back) it's 33,000 x 5 plus the 100,000, or 265,000. You can earn less; it's down to 10,600¥.
Take out the docwagon (don't forget to move medical costs to the variable costs), reduce the lifestyle, and what you need goes down. Run some truly ugly missions and your costs go up.