Deciding on your PPC budget can be confusing and a bit difficult to do, especially if you are new to the world of Internet Marketing. If you spend too much and get too little in terms of ROI's, then you're obviously going wrong somewhere. And, if you spend too little on the other hand, you'll find that many search consultancies won't even have a product or service to sell you. PPC is a powerful marketing tool that requires careful consideration for budgetary issues. You can't just pull a figure out of the air and hope that it works for your business. There are many ways to decide on a PPC budget. Here are a few steps that apply the “estimated cost-per-click, keyword” approach:

1.Identify the slightly general keywords and keyphrases within your campaign. Typically, these are those keywords that are only one or two words and have the highest volume of searches in the search engines. These keywords will also be the most expensive and will cost your budget heavily.

2.Your next step would be to obtain an estimated cost-per-click for these keywords. You could obtain these figures by using Google's Key Word Tool.

3.Based on these figures, you can now start to make a decision on how much you need to spend to obtain the clicks that you desire. However, it is important to keep in mind that this is just an estimation, and you will probably need to allocate a small portion of your budget to lower volume keywords.

These tips should help you get started on deciding how much to set aside for your PPC budget.

it depends on several paremeters:
1 - niche - each miche has it's own competition, and the PPC cost depends on it
2 - the number of words you want to get the 1st position at - the more words - the more money must be spent

I spend 50-100$ each day for adwords