Expenses, like what?
Domain name: around $10 for a fresh one. Many more $$$ for a quality expired one.
Web design: Depending on your requirements, you can invest from $2-$300 to $xxxx (even more).
Content: Quality content costs. The niche is also very important (for example, a 3k words article from a general niche will costs less than a well-researched 3k words article from the lawyer niche).
Backlinks: The quality of your backlinks will be in accordance with the size of your budget. Same here, the niche is important.
Generally speaking, you should have two budgets: 1 for the begin (creating website, etc) and one for backlinks, content, etc (this should be a monthly one).