TOOOOOOOOOOOOOOOOOOOO MUCH for fossilized carbon. Ugh :|
Actually, the diamond dudes "de Beers" started (at least they advocate) 2 months salary. However, there has got to be some minimum. I mean... if yer making $40 per week on a paper route, then a $320 ring aint gonna cut it.
It all depends. I know some girls who got a small ring b/c fiance is still in school. But then later, after he makes some bank, he gets them an awesome 5 year anniversary ring.
I would suggest at least 1/2 carat. No worse than K color. And clarity is less important, but I'd stay away from VS2 or lower. I think if you get 1/2 carate of VS1 clarity and J color... in a simple 14k gold setting, you could probably get by on 1 or 1.5 bills ($1k - $1.5k). I think... It has been a while.
Also... look into (and this may sound weird) a certified jewelwer on the internet. My best friend from high school (and also another guy I work with) found some jewelers in NY that were selling ISF (or whetever the certification is) diamonds... adn they are about half of what the local jeweler would cost. THey received them by insured mail, and even took them to a local jewlwer to have the checked out. A-OK. Then, they had them set in whatever setting they picked out from a local jewlwer... because they don't ream you as bad on gold as they do on diamonds.
Also, make sure you get a 6 prong setting, esp. if you get 3/4 karat or above. 4 prongs are likely to give you "diamond losing" problems in the future.
Hope this helps