If you replace with LG598378545 stone, the price difference is $427.65($746.85-$319.2). If you use the layaway program with the $50 rewards, it is $348.425(50%) and $348.425(50%). You paid $289.15 in #23719, so the balance is $59.275 and $348.425.
https://www.doveggs-seattle.com/collections/christmas-clearance/products/doveggs-2-01ct-round-g-color-si1-clarity-excellent-cut-lab-diamond-stonecertified-1