This is unfortunately a very difficult question to answer.
First I firmly believe you need to determine which types of traffic you are interested in. In short, first decide if you are interested in paid or free traffic sources.
If you are interested in paid traffic sources, your expenses will be much higher. As above I recommend investing in at least 1 domain (approx $10 a year), and hosting (approx $10-50 a month). In addition to this, you may want to invest in a tracker (or you may want to use a free one to start). You will also need to keep in mind your traffic costs, your initial budget for this should be approx $500-1000 to start out. Keep in mind, with this initial investment you may or may not find a winning campaign – we are not trying to discourage you, we just want to ensure we set the appropriate expectations.