I would say that depends on what kind of diamond you want. If you want an ideal cut stone, then I would say yes, a 1ct D/SI1 is out of the question. You should do a search here on PS with the specs of your choice to get an idea of what online prices are like. Expect the B&M prices to be higher...especially if you go to a name brand place like Cartier or Tiffany's, etc. Good luck!
If you want an ideal cut with lots of fire and brilliance, then yes. In my opinion, to drop down in cut you are sacrificing the sparkle- maybe look around the .9 mark or look to drop color to the near colorless range if you want to keep it at the one carat mark