Welcome to Harry Potter Answers. What would you like to know?

Uncle Vernon Dursley was an executive at a Drill making corporation. It would seem that the Dursleys were well off especially considering how much it would cost to spoil Dudley. Also, Vernon often dresses up and obtains a nice new car at one point in the series.

Not obscenely rich, but definitely upper-middle class, at the very least. Most of their wealth probably goes into expensive spoilings for Dudley.