i'd like to upgrade to full frame (D700). But one thing that is stopping me, is i don't see an affordably priced ultra wide lens for full frame nikons. i currently have a tamron 10-24mm ultra wide for DX and at its widest it is equivalent to a 16mm lens in full frame. my 10-24mm was pretty affordable ~$600. however when i look for full frame ultra wides around the 16mm focal length, they are insanely expensive, such as the 14-24mm nikkor. is there anything i can get for full frame ultra wide that can get me 16mm for under $1000 ? i have all the other FX ranges such as 24mm, 50mm, 70-300mm but trying to find an ultra wide for FX seems to kill the wallet.