Dang, the guy's pretty much said he doesn't want to build, he wants to buy. Let him have the X-Arcade. Sure, you can build one cheaper, but can he build one that looks as professional, and how much time and effort will go into it? Some people would rather pay a little extra and skip the work. Besides, he'll have enough work to do digging up an old version of MAME, a romset to match, a frontend, and configuring the system.
He can always replace the X-Arcade joys and buttons down the road if they bug him, and that'll be a lot easier if he's got a pre-built and wired CP box to work from. It woull make a good starter project, in fact.
Gavica: If you can afford a little more, look at the "Tankstick" instead of the "Dual Joystick" It adds a trackball, which will let you play more games. The USB 2.0/1.0 thing will not be an issue. But you might want to consider PS/2 instead of USB, if you decide to downgrade that computer to DOS or Win98 then USB support will be iffy. Also, don't sweat the video card, MAME doesn't make use of fancy 3d vid cards anyway, or at least not the old versions of MAME you'll be able to run on that computer.