This is all IMO. I have some experience with grass fed beef, not grain finished.
As much space as possible is better. You may be able to get by on 200 sq ft while it is young, but I like to have individual adult cows on at lest 1/4 acre each for their own sanity. However, they will eat the grass down so low that it is bad for the pasture. This can cause erosion and excess nitrogen runoff in the long term. To prevent this and save your pasture, you need to rotate even in the wintertime. A method that my neighbors use is to have a paddock area of about 400 sq ft as well as a few acres of pasture. They then raise calves in the paddock all fall and winter, letting them get it muddy and bare, and then release the calves onto the pasture in spring. Then they till the paddock and use it as a garden during the summers. Just to give you some things to think about.
For a weaned calf, prices change by week and by breed. For a beef breed calf specifically, expect to pay a lot more, especially if it is in good health. For a mixed or milk breed, you will pay less. Remember: you usually get what you pay for. I've seen people get bottle babies for $100 from dairies, but they were sickly little things. Usually, calves that are weaned are a few hundred dollars. $1 per pound is not unusual. You probably want a steer if it's for beef. Milk breed steers go for pretty cheap. Make sure you buy it castrated or know how to castrate yourself. Or, be prepared to pay a vet to do the job. Heifers don't have to be castrated, but they also don't have as fast of a growth rate or get as big.
Cows do MUCH better if they have friends. Without company, they will bawl all day and will want to be friends with you. If you just have one, you must spend a good deal of time with it for its mental health.
The ideal age for slaughter is between 12 and 24 months, depending on how much meat you want. Most people I know slaughter around 18 months. Some people buy weaned yearlings in the spring, raise them on grass acreage, and slaughter them in the fall.
Around here, I can get decent quality round 5x5 bale of hay for $20 to $30, not including delivery. I've heard that it's more expensive in other parts of the country, so you'll have to check local prices. These round bales are hard to maneuver as they tend to weigh a few hundred pounds, sometimes up to a ton depending on how tight they were rolled. A decent quality 5x5 round bale can last a 500lb steer between 2-4 weeks. It depends on the current temp, your cow's genetics, protein content of the hay, age of the hay, field or barn stored, etc.
Grain is much cheaper, which is why people use it. Around here, I pay $20 for 100lbs of 16% protein sweet feed. I have never fed grain as part of the diet, only as supplement, so I couldn't tell you how long that would last you.
No idea on processing costs, but it is fairly expensive to just have one cow done as opposed to a group.
Most cost-effective fencing for a steer would be electric, in my opinion. But, if he's not aggressive and if he has enough room, you might find it cheaper to use heavy-duty t-posts with some tight wire strands. Anything you can get for cheap or free would be the most cost-effective.
That's my 2 cents on the subject!
