Homepage On-Load Promo Pop-Up

I want a clean, lightweight pop-up that opens automatically the moment a visitor lands on my homepage. The overlay will show one promotional image, a short line of supporting text, and a clear call-to-action button that links to a URL I can easily change later... (Budget: ₹600 - ₹1500 INR, Jobs: CSS, Frontend Development, HTML, JavaScript, jQuery, jQuery / Prototype, User Interface / IA, Web Development)