The price issue is more one of choices not of "the Mac costs more". It doesn't cost more if you compare like stuff. If instead you say, well, Apple's low end laptop costs $1100 and I can get a low end Windows laptop for $600, well, that's true. If you stop there, though, you're leaving out the fact that a $500 laptop is somewhat lacking in various areas.

As for the "usable life" remarks, this can vary quite a lot from user to user and what you're trying to do with the machine, but at work we've been able to keep our Macs usefully employed (as everyday office machines) much longer than our Windows boxes.

No CA sales tax if you order from ExperCom. You may not be able to preserve the edu discount, but they should have some other discount available. And maybe saving the sales tax is a bigger savings than the edu discount.