Only if you value your time low.

It takes time to ensure the components are supported and work well together, and supported by the OS drivers.

So cost comparisons should either take into account integration-testing and driver support, or compare against a vendor that provides that (i.e., Dell, HP, etc).

I've tried the hackintosh route and it was fun for the first few weeks, but got tiresome after that. Windows or Linux with randomly chosen componentry is better, but not without it's pitfalls.