I don't think the system requirements are too high for a dedicated halo server, because you don't actually play the game on the dedicated server. Might want to look into cheap PC's if you really want a dedicated server, a 1 Ghz box should work..
Requirements:
Microsoft® Windows® 98SE/Me/XP/2000
PC with 733 MHz equivalent or higher processor
128 MB of system RAM
1.2 GB available hard disk space
8x speed or faster CD-ROM drive
32 MB T&L capable video card required
Sound card, speakers or headphones required for audio
Microsoft Mouse or compatible pointing device
56.6 Kbps or better modem or LAN for online play; broadband to run a server