Depending on the exact model, T43s are about $2.5k up. If you're confused, each series (eg, T43) have different models, all of which have different specs.
I think those two models they have on clearance were previously unreleased because they don't seem to be publicly available anywhere else. The $1.8k model is very similarly speced to the T43 I have but slightly better; it has Bluetooth, 80GB (I have 40GB) and a DVD-R drive. For comparison my model retails for about $3k.
If you look around the IBM site, very few of their machines are cheap. You don't find alot of people using them for that reason, but and theres a very good reason why they're priced like that.
One thing is Thinkpads have a reputation. I've gone through Compaqs (pre and post HP merger), Sony, and Dell laptops - for build quality IBM Thinkpads wins hands down. My previous laptop was a Thinkpad R40 and I didn't have a second thought about getting another Thinkpad when I bought the T43. Some laptops you look at and you know you don't want to knock it or bump it, the Thinkpads are rock solid.
I was with a friend working at uni in the robotics lab one time, and she accidentally dropped her T43 with the lid open onto a robot battery charger - those big ones with a giant heatsink, it landed straight onto one of the fins of the heatsink and it got nothing more than a bit of a chip. I think any other laptop would've had it and split open.
As far as support goes, I had trouble with my LCD once on the R40 and IBM organised a courier pickup and shipped it back working in 4 days. (It was under warranty still of course). So thumbs up in that department.
I've converted 3 friends to using Thinkpads now - one of them used to hate them because they of they way they looked ("too businessy" - and she works at IBM too!) but she hasn't complained since.
I'm actually surprised other people haven't recommended Thinkpads, but I would imagine thats because most students wouldn't have used Thinkpads before, because of both their price and their more formal looks.