Have you think about using a mac mini as your htpc? Arstechnica wrote an article about Mac mini HTPC Followup: Core Skills, if you want to use a Mac mini as your htpc, you should check it out.

Here are price comparison between different htpc cases

HTPC CASE / Black Desktop Case US $19.00 (0 Bid) End Date: Tuesday May-13-2008 17:14:50 PDT Bid now | Add to watch list

Zalman HTPC HD160XT B CASE W/Silent Power Supply & DVD US $405.00 (15 Bids) End Date: Wednesday May-14-2008 12:59:29 PDT Bid now | Add to watch list

THERMALTAKE MOZART IP HTPC ATX MEDIA CASE VF3000BNS NEW US $193.79 End Date: Wednesday May-14-2008 17:30:55 PDT Buy it now | Add to watch list

THERMALTAKE BACH HTPC ATX CASE VB8000BNS BLACK NEW US $119.25 End Date: Wednesday May-14-2008 17:30:55 PDT Buy it now | Add to watch list

Moneual Lab MonCaso 932B HTPC Case w/ Touch Screen NEW US $499.95 End Date: Thursday May-15-2008 1:57:22 PDT Buy it now | Add to watch list

Moneual LAB Black / Silver MonCaso 932T ATX HTPC Case US $499.95 End Date: Thursday May-15-2008 2:04:57 PDT Buy it now | Add to watch list

nMediaPC HTPC 100BA micro ATX 270W PC case enclosure US $2.09 (5 Bids) End Date: Thursday May-15-2008 15:34:28 PDT Bid now | Add to watch list

HTPC Case US $25.00 (0 Bid) End Date: Friday May-16-2008 9:33:05 PDT Bid now | Add to watch list

In Win BT610T MicroATX Low Profile HTPC Case US $0.99 (1 Bid) End Date: Friday May-16-2008 17:34:23 PDT Bid now | Add to watch list

Marant: Home Theater HTPC CASE / Black Desktop Case US $39.00 (0 Bid) End Date: Friday May-16-2008 19:21:36 PDT Bid now | Add to watch list

BL-6011 Home Theater HTPC CASE / Black Desktop Case US $39.00 (0 Bid) End Date: Friday May-16-2008 19:21:48 PDT Bid now | Add to watch list

nMEDIAPC 280BAV4 Black HTPC Case w/VFD 400w PSU US $50.00 (0 Bid) End Date: Saturday May-17-2008 10:34:50 PDT Bid now | Add to watch list

nMEDIAPC 280BAV W/VFD Black HTPC Case FOR PARTS/REPAIR US $20.00 (0 Bid) End Date: Saturday May-17-2008 10:52:22 PDT Bid now | Add to watch list

Silverstone HTPC Case Black -- More Than 1/2 OFF!! US $69.99 (0 Bid) End Date: Saturday May-17-2008 14:32:21 PDT Bid now | Buy it now | Add to watch list

*THERMALTAKE DH101 VF7001BNS HTPC DESKTOP ATX CASE NEW US $239.99 End Date: Saturday May-17-2008 18:41:44 PDT Buy it now | Add to watch list