I spent a lot of time researching diamonds. Knowledge > money when it comes to these things imo. You can spend 20g on a piece of shit diamond, or 5g on something very impressive. In the end I spent $3300 on what locally i couldn't find for under 15g (.80 vvs1 hearts and arrows round brilliant). I also ended up buying from bluenile because they list the dimensions of the diamond and had good selection so if you know exactly what dimensions turns in to a legitimately perfect cut.
I would also highly recommend keeping your gf in the loop or at least keeping her friends in the loop (not just one either), as a ring is a very specific taste, and you'll want to know you're buying the diamond and band she will actually want to wear. If shes not picky... perfect, but odds are she will be.
The first thing you need to know is 9/10 mall store sell shit. absolute garbage. I1-I3 diamonds are for industrial drilling, yet they sell u these shit diamonds in a ring and market the hell out of how you can get a 1 carat for 3g with inclusions so big you can spot them at a glance. And 1/10 mall stores sell stuff that is so expensive you could be blind and find a better deal elsewhere. stuff that is 10g in these stores i can find a better diamond online a 1/3rd the price. The shitholes usually have 90% of their diamonds in the I1-I3 range with the odd diamond in the SI2 range, maybe with a handful GIA rated.
Here is what you should focus on to get something good for the best bang for buck.
-not all certs are the same for grading. Go by GIA certs imo, and if it doesn't have a GIA and cheap, its probably such a shit diamond they didn't want to spend the $100 it costs to cert it as a GIA. other certs are useful for comparison but i found non GIA certs usually were far more forgiving. a J color with a GIA cert could be more white than a H color with a non GIA cert.
- clarity, if you want to cheap out or save money go with a SI1. But never buy anything worse than a SI2 that is GIA and higher if not GIA. No one can tell teh difference between a SI1 and a VVS2, or even a IF with the naked eye. (I personally went with a VVS1 because i like that it is almost flawless, but still has one tiny spec of a flaw to tell that it is a real diamond)
- color, whiter = more expensive. Take your GF diamond shopping and see if she can tell teh difference between colors or if she cares. Never buy anything worse than an I color GIA IMO, as it will be yellow enough anyone can spot it. DEF is a waste of money IMO unless you are baller or she is going to be comparing against other baller's purchases... and cares. I'd say stay away from DEF because color makes a huge price difference imo. I went with a I for color because H and G significantly increased the price, and while i can tell the difference between a I and a G side by side, we couldn't tell which was which by themselves (I could tell a D from a I by itself though, and comparing them there is a pretty big diff, but i also couldn't tell a D from a F with comparison). J I could pick out by itself easily though.
-carat size. whatever size floats your boat. IMO you can get a diamond in the .7-.9 carat range that looks decently big for a very affordable price. If you're on a tight budget you can get an absolutely amazing diamond for 0.5-0.6 for very little money. Dont get anything smaller than .5 imo as the savings is not huge. I went with .8 because azn wife factor and there was no .88s that met my criteria for dimensions. if your gf has a tiny finger she may not want a large diamond too as it might attract too much attention. my wife didn't want a 1 carat because they looked too big to her.
- cut. this is the hardest and most important thing imo, and where knowledge comes in to play. If you want something to sparkle like someone threw a flashbang into the room, you want a round brilliant hearts and arrows dimensions diamond. Avoid any other cut imo because light will not reflect out of any other cut like it will out of a round brilliant. People pay big bucks for hearts on fire diamonds because they sparkle so much, which is just clever marketing and markup on diamonds that you can find on your own if you know what dimensions create a perfect storm for giving the most sparkle.
As for the band, you can buy the band and diamond separate. I had no problem finding a highly recommended jewelry crafter in edmonton that had no problem making any ring i wanted and using a diamond i brought him; i'm sure calgary is no different. He basically said if i bought the diamond from him he'd charge me $200 for materials cost for a custom ring because he'd make his profit on the diamond and it would only take him maybe 2 hours of labour, and if i brought him a diamond he'd charge me 1000ish, which was still a good deal cuz the ring he was duplicating was more than that. My wife wasn't too picky, we ended up cheaping out and going with a $200ish band from blue nile when i got the diamond.
the main website you need to read before looking at diamonds IMO is this. look for these dimensions and you'll end up with a diamond that will sparkle like crazy, and if you browse the thousands of diamonds at bluenile or other online stores you'll be able to find something decent. ALso, do not fear buying online. If you get those dimensions, the same color grade u see in stores your happy with, and anything SI1+ you'll have a the diamond you expect show up being exactly what you expect.
http://www.heartsandarrows.com/heart...l-cut-dna.aspx