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HP/Compaq Proliant 5000. 200 MHz (may be available slower) is a possibility at $300 USD on eBay plus shipping it across the border to Canada. 2 PCI busses with 5 slots (2 shared with EISA), max 4 GB ram, Pen Pro CPU, 5 bays in a rack-mount, 4 in a tower (may be other options but I haven't got the manual for this unit).
These are great servers. Ran one as my web server for a year and it did not let me down. Might I suggest for your HDD requirements a Compaq Proliant Storage System U1. I am not sure at the MHz rating for the inside components, but they are of the same age as the 5000 you are looking at. The caddies for these things are really cheap to, on Ebay one could get one for as little as $5 AUD.
If the MHz are ok with Disk Arrays, you probably could use any shelf. A search on ebay also revealed these servers that could help.
http://cgi.ebay.com/Compaq-Proliant-2500-2500R-Processor-Cage-Dual-200Mhz_W0QQitemZ230127564041QQihZ013QQcategoryZ56092QQrdZ1QQssPageNameZWD1VQQtrksidZp1638.m118.l1247QQcmdZViewItem http://cgi.ebay.com/COMPAQ-306591-B21-PROLIANT-5500-PENTIUM-PRO-200MHZ-512K_W0QQitemZ330204744058QQihZ014QQcategoryZ11175QQrdZ1QQssPageNameZWD1VQQtrksidZp1638.m118.l1247QQcmdZViewItem Regards, Julian