1. Prices depend on your dealers and the quality of the weed. Ask your friends about that one I assume you'll have to go through one of them to buy your weed anyways. You could buy an ounce dealers give price breaks with bigger orders sometimes. But first off i suggest buying a scale that way you can know ur not getting ripped off. About .5g (3.5g in an eighth of an ounce) should pretty easily get you high.
2. You will know when the bowl is cashed basically by the taste. When you get that hit and you say to urself hmm...that tasted like shit you know its cashed.
3. Don't get your lips totally on the bowl if you're smoking with others as far as bowl etiquette goes. I'm assuming you already know how to use the bowl, but i like to cover and release the carb while hitting it so i can get a good airflow and plenty of smoke.