Kaizen probably makes the nicest overall Kettlebell for the price. Sleek design and very smooth and thick handle. The sizes are limited and in kilos but they have all the necessary sizes.
However, Kettlebell King sells Troy Barbell Brand Kettlebells for the cheapest you'll find shipped anywhere.
But these are without a doubt your best options. I have two pairs of Kettlestacks and the idea is great to be able to adjust them, but your better off getting the real thing.