Like Basskiller said, 1carat diamonds can cost anything you might want to spend.
Last month I bought my wife a 1.33carat diamond that ran me $4150. And I'm a jeweler even!
Just remember - if the deal seems to good to be true, it is.
ALWAYS request a certified diamond graded by the EGL, GIA, IGI, or HRD. For added 'security' some of these labs are laser inscribing the girdle of the diamond with the report # to help match the two together.
But back to the original question. Buy the ring, and close the deal. Juice can wait, but she might not.