This is a comparison of 0.75ct ideal cut, F color, SI2 clarity round cut diamonds (click the dollar amount to be taken directly to the diamond):

James Allen: $2120

Blue Nile: $2634

Abazias: $2735

Brilliant Earth: $3010

These diamonds are independently inspected and graded by GIA/AGS, which means you can trust their quality. The quality of these diamonds is identical--the only thing that is different is the price.