Is this even cost effective doing for the dual processor versions? I understand using an i7 would be cheaper for the single cpu, but how much savings are we talking with the dual cpus?
If you were to buy the parts straight from websites such as mac-pro.com and applecomponents, macrecycling, welovemacs and macpalace, then no it's definitely not cost effective because they will nickel and dime you to death. I've been looking for 2 months now on eBay and strike when something I need is listed at a cheap price. I struck gold with my case: 190 for 2009 chasis with PSU, fans, and all internal casing. If you were to buy those individually like they sell them on those sites, you can expect to pay 300 for case, 300 for PSU, 30-50 per fan, internal cages could add up to over 100.
Now with that said...the CPUs are the deal breaker. If you buy them at retail, you'd be spending 3k and that's just not cost effective. They will be the last parts I buy and I will take as much time as I need in finding them for at least half the retail price. May take me months but just have to be patient. I figure this is my new hobby, so it should last for a little while