You need to sell them earlier to reduce the cost if you want to turn a profit.
I sell POL pullets at 5 mo old for $14.00 each. ($20 for rarer breeds.)
Using the numbers above, the cost of feed is $320 for 100 birds, or $3.20 each in feed:
For Oct - Nov you would need 4 lbs per bird x 100 birds = 400 lbs. Divide that by 50lbs = 8 bags x $10 = $80 minimal
For Dec - Feb you would need 12 lbs per bird x 100 birds = 1200 lbs. Divide that by 50lbs = 24 bags x $10 = $240 minimal
You basically double the expense of feed by trying to keep them to 7 months. So don't keep them that long.
Secondly, you need to be in it for the long haul. Considering the cost of pens, feeders, waterers, etc - you have to raise batch after batch and spread these costs over many, many birds. And really, those 'housing' items will last for years and do not represent the cost to raise a single batch.
You might also consider raising them to the started pullet age - 8 weeks. I sell pullets that age for $8 each.
Using the numbers above, the cost of feed is $80 for 100 birds, or $0.80 each in feed:
For Oct - Nov you would need 4 lbs per bird x 100 birds = 400 lbs. Divide that by 50lbs = 8 bags x $10 = $80 minimal
Edit: typo