It will be cool if we can create a page with pull down menu for the components and total prices will be calculated at the end. Then update the price database every 3 months.

Option of selecting rig by price (maybe price brackets) or by purpose, also specify if need monitor or OS or peripherals. But someone need to actively look up the different offers in Garage Sales, unless the sellers are willing to send in the updates themselves.

Eg:

Default start page to include: Expected budget, option if to include monitor/OS/peripherals, and purpose (general/gaming/graphic workhorse/mixed)

Then upon selection, a preset configuration of recommended parts (for the set budget) will come out. At that page, user can select what they want to change as each component will have pull down menu with parts (and average price)

At the end, the new total price will be calculated, with info on where to get the components for best price.

Most of the parts remain quite the same in 3 months, such as processor, hard disk and PSU.
Only graphic card and occasionally mobo have more frequent price updates. Even then, monthly update would be sufficient as the price revision only goes about 4-8% either way. Then there's the promo period by Garage Sales people.

Question of update comes secondary to motivation and know how for the setup of such a webpage.