Micro ATX cases normally cost a bit more and only run 150-250w. The PS is also a Micro ATX power supply.
What is wrong with the Shuttle cases. $300 for a case, powersupply, motherboard with integrated sound, video, nic, USB 2.0, FireWire, and TV-out with CPU cooler and case fans included is not that bad of a deal. The new nForce2 board one is just about out (some web sites got some reveiw samples this Holiday). If you assembled the system yourself with good quality parts, you are looking at a $100 case and $150 PS, plus some fans and heatsink you are looking at about $300. Now if you get a cheap featureless motherboard and a cheap'o genaric case and power supply, plus a junk heatsink, then you will likely have an ugly cheap computer with possible stability issues, but you could get them for half the price. These Shuttle systems are pretty well made and those surver power supplies are only rated for 200w, but I have seen them running a 3Ghz P4 and a Radeon 9700Pro. Those two alone draw over 150w. The only issue I have heard about is the cooling for the hard drives and this new case is supposed to improve the cooling a lot.
The only other good option is to make your own case. I was looking at server PS adn you can get a nice 300w Sparkel for $50-60 They are the same depth and height as a CDROM. If you put the two together you get a box less than 2" high and 10 inches wide and deep. A Micro ATX board runs about 9.5"x9.5". Find a box 10"x10"x7" and cut some holes for someCDROM in the front and PS in the back. Put down a sheet of insolating foam like what comes with a motherboard most of the time and drop the on top. Zip-tie it in place. Cut a blowhole in the front left and back right side and add some fans. Cut a spot for the I/O sheild and any expansion cards you want to have and add a few buttons for Power and Reset. I was looking to make one out of lexan and use the clear LED fans. Alsmost any Micro ATX motherboard would have worked.
Here is a picture of the box I was looking to make:
AMD Phenom II x4 945 3Ghz | ASUS M4A77TD | 2X WD 1TB SATA 2 hard drive | 2x2GB Corsair XMS3 | nVidia GeForce 8800 GTS | ATI TV Wonder Theater Pro 550 | Antec P-160 case | Antec 650w Earth Watts | LG Blu-ray Super Drive | LG DVD RW | Windows 7 Pro