Well, hot on the heels of the eeePC is the DecTop.
The specs are a bit lower (366MHz Geode, 128Mb RAM, 10Gb HD, No Ethernet), but DEC will sell you a pack of 4 for $75 each (including keyboard and mouse). This takes the cost of our theoretical platform to around £45 + £85 = £130! ( or £520 for 4).
However, (and this is a big however), the DecTop isn't new. Actually it's an old AMD concept called the PIC, designed for developing countries, which doesn't seem to have been successful in the marketplace. The prices Data Evolution Corporation are offering are in fact sales prices, which kinda implies they'll stop selling them soon!