I've bought several refurb'ed thinkpads in the last couple of years.
More than a couple have died within about 9 months of my purchase.
Moreover, I get the impression that the T30, because it runs hot and
can have memory issues, is more failure prone than most. I don't know
about a 3rd party warantee, but I would also consider it, especially
if it is one +$100, which is much cheaper than ante-ing up for another
$400.

My gut feel is that $400 for that machine would be cheap. However, if
you go to Ebay, you can quickly see what similar machines go for. My
current primary machine is a T43p for ~$1k and I love it. It's on a 1
year IBM + 2 year 3rd party warantee. Once I'm past the 1st year and
it's still running, I will be happy.