It's really hard to say on the pricing. For example I got my X220i the first day for $750 shipped. While it has dropped below that price a few times, it's remained a pretty good price. The T420s on the other hand was pretty expensive when released, but has slowly dropped in price over time.
If you're looking for value, the Dell Outlet is tough to beat. Something like the e6420 is a solid workhorse if not as elegant as the T420. You can probably get one for less in the Dell Outlet, especially if you can wait for the coupons that Dell offers in the Outlet with some regularity. There's a thread in the deals forum dedicated to Dell Outlet coupons. You may wish to check it out. Lenovo also sometimes has sales as well, but Lenovo Outlet purchases are limited to a one year depot warranty that cannot be upgraded. The Dell comes with a three year warranty standard.
Buying on eBay is always a little more dicey than directly from the manufacturer. The item linked is New Other, which can be hard to determine what that is.