Check with Shannon Fine Jewelry on 1960 in the Champions area. They have some really good deals in the consignment case and will deal on them if they've been sitting long enough.
OK, I have gone thru this several times and tried many of the above mentioned sites but the cheapest and best quality I found was thru Union Diamond www.uniondiamond.com ask for Leah Cawley. They have diamonds and settings for all price ranges. I saved $4k on my wifes ring!!!
Find some divorcing wife with a big rock that wants to sell it for lawyer fees and a new purse. Then get it mounted on a setting of her choice! Buddy did that and bought a 3 carat round diamond for half of what bluenile.com and James Allen wanted for it. She was even nice enough to have it appraised before he wrote the check.
On Hwy 90 in Rosenburg, I bought on there 27 yrs ago. I can walk in today what I bought that day and its still on file and everything else I bought. Great people and product.
Go to a retail store and learn all about the 4 C's and see where you are willing to be flexible. You may be willing to give up a grade of clarity to get a better color. IMO color and cut is more important than clarity since nobody is going to put a magnifying glass to the ring nobody will ever know if there is a tiny flaw.
I bought my wife's from www.novori.com and had a very good experience.
I second diamond cutters international. They know their stuff when it comes to diamonds and won't steer you wrong. They do a lot jewelry for pro sports players and other stars. I used Grayland Noah and at the time I had my wife's ring done he had just ex rockets player Tracy McGradys wife's ring. They also at the time had their $1,000,000 rubix cube they designed and got to hold.