Spot Runner, a start-up that aims to make TV ads affordable for small businesses, has raised another $51 million from investors as it plots an expansion into other media.

The fourth capital infusion, which will be announced today, brings the Los Angeles company’s total funding to more than $110 million, including $40 million in October 2006 from major media and ad companies like WPP Group, Interpublic Group and CBS.

Spot Runner initially made a splash with its plan to make it easy for small businesses to run local TV spots for as little as $500. The trick was a library of stock ads that clients could customize without going through the trouble of creating their own.

Since then, the privately held company has been seeking to extend its local ad expertise into radio and the Web and overseas.

“This is about getting some dry powder to invest in some platforms we’re building,” said Spot Runner CEO Nick Grouf.

New investors include UK media giant Daily Mail and General Trust, Spanish-language broadcaster Grupo Televisa and luxury goods giant Groupe Arnault/LVMH.

Despite its impressive roster of investors, some critics grouse that the company is more hype than substance. holly.sanders@nypost.com