jeweler's row, sansom street in philly. i bought my wife's diamond local, but the place is out of business now (sold their stuff too low - near cost). there is a place close by in toms river that runs a special between december 25th and january first - if it snows, your purchase is free (some insurance company uses the farmer's almanac to adjust their rates). i think you have to buy between dec 1 and 25th, tho. my dad knows a few people in the biz that have their own shops at home as well as what they do during the day. if you are really serious, i can get you some numbers.
experience says don't go to a mall. their stuff is overpriced and not of the best quality.
do your homework online, then go to a brick and mortar.