As stated there are many places and the members here are a great help.
I watch for sales, buy used equipment with warranties, etc
I shop the PM sponsers, Optic Planet, SWFA, etc
I'm aslo a member of DVOR which is part of optic planet and they have daily clearance items at 10-70% off which is exclusive to members only.
It's free and you're not obligated to buy. Here is an invite for anyone interested:
http://www.dvor.com/s/6p0gkd.html
Just a few weeks ago I bought a Trijicon accupoint 3-9x40, Green for 585 bucks and bought two top end mounts for half of what everyone else was selling them for.
PS: I agree with alot of what Meat Hunter has said. A lot of people over torque or in some cases under torque which can cause problems. There are tools that can make it easy and now days there are instructional videos on YouTube, Midway, and many other resources as well.
However, if you are not mechanically inclined, etc, take it to a good gunsmith and not the gun nutt next door.