No. You can spend as much or as little as you want, within reason. However, your return will always be proportional to the amount you spend.
To give some rough reference points, large, internationally known e-commerce sites, such as Amazon or Ebay, can easily spend millions per month on clicks. However, if you’re a sole trader offering a business service in your local area, you may only need to spend a hundred or two to get all the enquiries you need. A small e-commerce site working in a niche area might spend a few thousand. The important thing to remember is that what you get out is proportional to what you put in. Making that proportionality as favourable to you as possible is where aPPC management agency such as ours comes in.
The great thing about a pay per click campaign is that the budget is very flexible and the return on investment easily measured, so you can adjust your spending to take into account seasonality, market conditions, promotions, etc.