OK here is what I know about diamonds, besides being too expensive. Color, cut and clarity. I took some man made diamonds to my jeweler and he wanted NOTHING to do with them. Said they were worth nothing and he will not deal in them. Somebody that wants 5500.oo for a lab diamond is selling you just the gold, according to my jeweler.
2Karat is overboard IMHO. I would be looking for a 3/4 to 1 K, Color D, VS1 rated if you want a fine stone, and that will cost you plenty.
Everybody knows a guy who knows a guy. Buy a loose diamond based on getting appraisal before you buy and have it set. If you can follow that and get the appraisal, you can save a ton of money. There is at least a 400% markup in jewelry. so think about in the 5500 fake diamond a 400% is worth just the gold. Gold is 1850.00 or thereabouts an ounce.
Do your homework!!!