I've had pretty good luck getting Magitronic (Focus) keyboards for around $20-$30 each, including shipping.
Lately I've been hunting old Toshiba laptops for their Alps-compatible keycaps. Some pretty neat color combinations, and the limited selection of modifiers wouldn't be as much of an issue if you're going for a 75% layout. The beauty of these key caps is that they're all doubleshots, from what I've found so far. Some have pad-printed secondary legends, like on the fronts of the keys.
The article that led me to the Toshiba source:
http://deskthority.net/photos-videos-f8/toshiba-t3100-t5200-t4711.html From the article:
"From what I found on all the Toshiba T-series laptops, the following have ALPS compatible keycaps. T1200, T2100, T3100, T3200, T5100, T5200"
I haven't found any of the pictured graphite/orange modifiers, but I have almost complete sets in a nice cream-coffee color, and a set in gray w/graphite modifiers.