Amazon offers the Kitchens of India Butter Chicken Curry Paste 3.5-oz. Box 6-Pack for $9.38. Order via Subscribe & Save to drop it to $8.91 and score free shipping. That's $5 under the lowest shipped price we could find elsewhere, although it was a buck less three weeks ago.
Be sure to cancel Subscribe & Save after your order ships to avoid being billed for subsequent shipments.