I got the Manfrotto 190XProB + 488RC2 head. Totals over $300. Not too ex but it's an alu tripod.... not carbon. It takes my D40x and 70-300mm well. I have another macro lens which totals out the entire setup at 1.5 kg or so and this tripod + head works fine.
Check out the manfrotto website. They have a useful configurator that can help.
There're other makes like Benro, Velbon, Slik and of cos, the high end Gitzo.....
Need something to take 2-3 kg weight and you should be good for at least the D40x plus some upgrades.