The only thing I will spend large $$$ on is my camoflage set-up. The proper camoflage matched with the environment will give you the ability to stare directly into most players' faces and watch them continue on there way without giving a second look.
It's usually not more than $60 for the surplus soviet stuff, but gets stupid expensive when it comes to the replica WWII patterns.
Masks are also important, but my V-force Profilers haven't died on me and don't think they ever will. I also have a gas mask, but it's not exactly sealing with the beard I'm growing. I had forgotten how much I liked to breathe lol.