I use Anandtech and Tom's Hardware first and foremost when it comes time for benchmarks and tests and reviews. If I need additional benchmarks or more niche data, HardOCP and Guru3d are also good resources to tap into. When it comes time to purchase, Newegg is the first and often times the only stop. I've ordered from zipzoomfly and tigerdirect in the past too, and they have worked well.
My current PC is an amalgamation of parts from over the last 6 years, so I can't offer any helpful info when it comes to its price. The best piece of advice I can give is that before you build a machine, know what the purpose of the machine is going to be and select parts specifically for that purpose. You do not need a high-end processor or graphics card to read email and listen to music. You do not need 16 GB of RAM or a hexacore CPU to play 3D games. You do not need a blu-ray player if you won't be watching blu-ray discs. You do not need a RAID of SSDs if you're not doing anything disk I/O intensive.
With that said, it's also helpful to plan for any future tasks in case you do end up pursuing them. For example, do not buy a wimpy power supply if you think you might want a powerful graphics card next year. The wimpy power supply may be cheaper now, but it'll cost you in the long run if you need to buy a second, stronger power supply.
You will save money by adhering to this advice. Saving money is good. You like saving money.