You can spend just about any amount of money on pay-per-click advertising.
One of the other things that differentiate pay-per-click from SEO is that you only pay for the results. In a typical PPC model like a Google AdWords campaign, you will pay only when someone clicks on your ad and lands on your website. You can spend just about any amount of money on pay-per-click advertising. Some companies may see results from investing just a few hundred dollars, but plenty of large companies spend tens of thousands a month on pay-per-click.