I'm on East Ladder and a CtA is roughly 1 HR per BO level. For ones with 6 BO, the price will be more; adding a handful of HR to the price depending on the BC level. I see many 6 BO CtA's go for 8 HR. I bought a 6/6/2 one from gorash for about 10 HRs.
Take advantage of the way the three spells work. If you can get some distance, set up some spirit fields. Try shooting them out as an arc instead of a straight line as it gives you more screen coverage. Then you can use spear/teeth to stun them (great if spirits are right behind them) or lure them to your spirits (shooting spears ahead of them so that they run back into the spirits). You can also make a large spirit field and teleport inside them to lure people in (kind of like a trapper but harder).
If you're using spear off-screen, don't aim directly at the X as it is slightly off the target. The best way to do this is practice. Have a friend stand off screen and tell you how much you need to adjust the aim. Do this for different angles and positions (at least 8 - top, bottom, left, right, diagonals).
If they're a running character, shoot spears in front of where they are going. You'll probably miss the first few times but it will get more accurate as you get used to their speed. A fun game would be to have a pally charge around you in circles while you try to hit them (great for practicing against auradins that charge around).
If you go to soulless child's guide, there is a section on spear sniping. It was written for necro v necro but it applies to sorcs and other classes as well.
