well, the way i can usually judge if it's good or not is:

1. look at the color (brighter green hues mean it's good most of the time)
2. look for little red hairs on it
3. look for teeny tiny almost-clear crystals on it (NOT white powder! that's PCP, NIGGA!)
4. smell it. the good stuff around here lately has a bit of an almost-piney smell to it, but you're probably not experienced enough to be able to pick out the certain smells it has to it
5. SMOKE THAT SHIT!!! lol

and, as far as prices, if you know the exchange rates...

.5 gram (maybe 2-3 pipes for you)- 5 USD
1 gram (4-6 pipes)- 10 USD
eighth (3.5 grams)- 20 USD

may be different in your country, though...