I will offer my services on selecting a quality diamond with good specifications that is the largest possible without sacrificing quality, and for the least price. I am diamond certified and have worked in the business for years.
Your best bet is to buy a certified diamond online the markup is 15 percent versus stores 300-400 percent, the quality and selection are better.
Great effort on the other answerer but, Pearls are delicate and not at all suitable for everyday wear in a ring.
The E-rings are all very poor quality with an inclusion clarity meaning it will look very imperfect with lots of visible black spots (carbon deposits). Two of the E-rings the primary diamond is microscopic at 1/5th carat.
Suggest a solitaire setting in white gold for 245.
http://www.adiamor.com/R-999-R2739-1.htm
or a platinum comfort fit for 488
http://www.adiamor.com/R-625-R2614-1.htm
http://www.adiamor.com/D-8842901.htm
.51 pear, D/SI1 measures 6.75mmx4.61mmx2.87mm for 1019
http://www.adiamor.com/D-8523287.htm
.51 oval, D/SI1 mesures 6.36mmx4.71mmx2.76mm for 1035
http://www.adiamor.com/D-8842654.htm
.57ct oval G/VS1 mesures 6.42mmx4.68mmx2.93mm for 1102
http://www.adiamor.com/D-8517965.htm
.53ct oval E/VS1 measures 6.59mmx4.64mmx2.76mm for 1131
http://www.adiamor.com/D-8763766.htm
.56ct oval F/VVS2 measures 6.63mmx4.82mmx2.83mm for 1176
http://www.adiamor.com/D-8945381.htm
.51ct pear G/VS1 measures 6.86mmx4.55mmx2.76mm for 1172