This is a bit far from the initial idea of creating a custom workspace but follows nicely from the estate sale bit...
Another good place for furniture (and all sorts of other cool stuff I might add) is a college or other large place of higher learning. Mine has a monthly "surplus sale" where they sell off anything and everything the various portions of the institution no longer want. I just picked up a really nice desk in a similar need for work space. Its huge and solid wood, cost me $50 (not the best deal I've seen at the sale but worth it in my opinion).
and heres a picture because its so pretty... (for an idea of the size its 5 feet long and 34 inches deep)

It looks so empty... just got it so there hasn't been time to accumulate much and had to take the lamp off it to light it.
oh and huzzah for my first post >.>