From the advice I've seen on Gamer's Nexus, it's currently cheaper to buy pre-builts at the moment since their systems are priced from RAM they for 3-6 months ago.

As much as I hate to admit it as I don't like Linus, LTT has some good secret shopper episodes (and so does GN to a lesser extent). Just watch the conclusion episodes where they rate how each system integrator performed. Stay away from big brands like Dell, HP, etc.