This is a comparison of 0.5ct ideal cut, F color, SI1 clarity, cushion cut diamonds (click the dollar amount to be taken directly to the diamond):

Brilliant Earth: $1000

James Allen: $1050

White Flash: $1218

Abazias: $1325

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.