How to represent a numeric input that is limited to increments of some number

I have a requirement for a form that restricts a field value to fixed increments of 50 and I'm not sure what would be the most elegant way to represent that constraint in a meaningful fashion.

The simplest solution that comes to mind is a jQuery validate method combined with some server-side logic that is tied to a normal text field input. Other alternatives that come to mind is a number picker of some sort (I don't know of one currently) that advances in set increments or a drop-down list with a fixed number of values.

Any other ideas? What would feel most intuitive to you?