well heck, thankya Joey!!! 
 
just a few months ago (ok, over a year ago) I decided my wedding set needed to be replaced. I just took my beautiful great quality original diamond and had it re-set in a big, beautiful, platinum thingy. Just a couple of grand, with the new band and all. 

and do you know what they did??? (this was not at Eiseman's, my real jeweler 

 )
for $35 buckaroo's they put a CZ (!!!!!!!!!!!!) in my old ring. wow! can you believe it??? You absolutely cannot tell the difference between it and my good diamond. (when just casually looking at it)
I couldn't believe it and man was my hubby happy.... and yes... i did order my 500 just one month later. 
You CAN have your cake and eat it too. 
 
  
ok. sorry to hi-jack. 
 
 
I would most certainly get educated before being suckered at a chain type store. 
They generally have decent, run of the mill diamonds. 
But if you want a really good 3 carat, get online and do some research, THEN visit some quality jewelers. 

K
(i'll step out of here now) 
 
ps. i would surmise that a good diamond is around $10k a carat, and 3 carat stones are much rarer, harder to find. 
good luck!
I have a friend who has one (one carat per kid) and I could discreetly ask her or her hubby what it cost per carat.