EUR166 for a Via EPIA C3 800, EUR110 for a Starex Mini-ITX case, EUR55 for 256MB of PC133 SDRAM, EUR57 for a LiteOn 16x48x DVD/CD-ROM, EUR115 for a Western Digital 80GB HDD and EUR50 for miscellaneous expenses brings me to the grand (and currently unaffordable) total of EUR553.
Maybe I should rather upgrade my home network infrastructure with a new 100Mbit/s switch and wait a few years until the components above are available for a song. :)