Here's my Northgate Omnikey 102 that I picked up at a local thrift store for seventy cents. Since I am still relatively new to the world of mechanical keyboards, I actually had no idea what this was when I purchased it.
Between the cleaning supplies, adapter, and PS/2 wire, I have about $18 into the keyboard as it sits right now. For the time being I had to replace an inoperable white Alps switch with a black Alps, but under regular use the difference is more or less unnoticeable.
Before:




And the after. The variations in color seen in this pic are far less noticeable in person.

Not bad, eh? Now if I can only find a darn Model M!