I crunched a bunch of numbers on this last year, and came up with a very similar number to yours - 300 head.  I made the assumption that harvested feed would be purchased or custom harvested (if you're doing all your own you should be charging yourself the opportunity cost anyhow) so that all family labor could focus on the cows.  At 20% equity in the cows and land take home income would be $60,000.  With cows and ground paid off take home income would be $300,000.  I'm pretty sure I based prices on the last 5 years average of feed and cattle markets.

The widely varying definitions of what constitutes a "comfortable living" makes this an unanswerable question.

Another way of looking at it:

University numbers a few years ago said it takes $500/yr to support a cow. That number is no doubt closer to 600 or 700 now. Lets say it takes $650/year to support/own a cow without arguing about what that includes. If we have a spring born calf sold in early winter at 650 lb or so, lets say it cost 50% of the cow or $325 to bring a calf from birth to 650 lb in the early winter.  So the cost per pair is around $975 or round it up to $1,000/year for a cow and 7-8 month old calf.

CME Nov 15 feeder calves are currently at $2.06.  Selling a 650 lb feeder calf in Nov @ 2.06 = $1339. gross income from the pair - $1000 annual expense for the pair = $339/year profit.

Theoretically a USA average herd of 50 cows selling 50 calves in the fall per year would produce a net income of approximately 50 x $339 = $16,950/year.

I believe the above University (Iowa State and U of MN were where I heard this type number a few years ago) numbers include some land amortization etc. The numbers are probably for an existing herd and does not include buying startup cows at today's prices.

Then to the original question: is $16,950/year net profit from a cow/calf operation a "comfortable living"?   Maybe a reasonable retirement income or supplement to off farm or row crop income?

By this logic, 100 cows would produce a net profit of about $34,000/year.  200 cows selling 200 calves/year would then produce a net profit of about $68,000/year.

edit to add: If 650 lb calves sell for $2.60 in the fall that 50 cow herd net profit moves from $16,950 to $21,400. Still no windfall but a reasonable supplemental income for more folks. But you still have around $100,000 (50 cows x $2000/cow?) tied up in cows alone to produce around $17k/year.

This also points out why calf prices need to stay up or there won't be many feeder calves to buy.  Even "dryloting" cow/calf....  how much facility investment and operating costs are you going to be able to invest and amortize to try to reduce the $1,000/year cost to produce one calf per year????

It may seem to be optimistic, but it sure wouldn't be easy.  Just to get to the 20% equity starting point in cows and land would require over $300,000 cash; that's not going to be very easy for anyone.
JustIf is right, the successful and profitable ranches are usually multi-generational - it just takes too long to pay down all of the debt.  And hopefully you raise 'em right so they don't fritter it away.

I think thats close on you'er numbers Jim 350 profit was close last year my depreciation was high so if calf prices drop so cold my depreciation.

But I can go ride around in the ranger looking at cows take em salt mineral really enjoy the day Do you think Waren Buffet enjoys life that much? I dont have much money but I would dare to say my life is richer than his. 

So in addition to your 2500 acres of row crop, how many acres do 2500 hd of cows need in your neighborhood?  Go big or go home!

+100
I don't think many of us are in this business to get rich in dollars, but we can all be rich in experience and memories.

It can be done if you want it bad enough. I started in 2004 with a lone for 10 cows and owned 40 acres. If you want it go get it and don't sit and talking about it or saying you never had an opportunity. I have not inherited a penny.