The best prices I have seen for tanks is The Pet Place in Lancaster PA. I actually drove there to get a tank and some equipment last year.
They list a 125g Perfecto w/2 corner flo for $399 (black or oak). They also have 125g All-Glass Reef Ready for $399. The All Glass would still need the plumbing for the overflow. The Perfecto's come with the plumbing.
Tax in PA is 6% so it would cost $424 in Lancaster. Locally with tax would be $459. Unless you go next weekend when they have their annual sale and the perfecto tanks are 10% off, saving another $42.4 with the tax. You would need a good day to drive there get it and drive back plus the gas. If you go during the sale expect crowds. I don't know if it is worth it to save $35. You could however let your LFS know you can get it somewhere for $399 and they might be willing to negociate a little. Maybe delivery, throw in some extras.
I am not a good negociator so I usally pay the asking price, but that is me.
Good Luck,
Dave