D.I.Y Kits are getting more sparse these days as the makers are putting little chips on there cartridges.
Yes, these chips can be "modified" but its not something that the average guy can do, without all the tech to go with it.
So, as said, look on ebay for the compatables, or go to a Cartridge shop, there are loads around.
HP Cartridges have always been expensive though, the compatables are too when you compare them with Canon or Epson.