An investment is usually made with the expectation that you will get that money back along with even more money.
So if you spend/invest money to start the blog you need to determine how you will get your money back: will someone pay you to place advertisements in your blog?
Since you need to wait a whole year then you can figure out how much money you need to receive each month (on average) to cover the cost of your investment and the return that you expect. And do not forget the value of your time - that is also part of the investment.
First figure out how much you need to invest with regards to ISP services, equipment, website/blog hosting etc.. Then figure out who, if anyone, may be willing to pay to advertise on your blog or otherwise pay for or subscribe to your blog services. Plan on needing a few months to prove the worth of your blog and the growth of readership before receiving any such income.
Summary: Can you, and how can you, really earn bucks from your blog and enough of those bucks to cover the costs. Plus have some left over for the purchase of new gear? That is what you need to figure out.