Slim pickin's these days - it depends on what GPUs you can find for a reasonable price.
If you can find 3x Radeon 270x's in stock for around $200 or less per card, just about any AMD AM3/AM3+ motherboard with at least 3 PCIx-16 slots, a Sempron 145, and a ~750 watt power supply, you are probably looking at $800 give or take for ~1.3MH/sec.
Yeah, sounds 'bout right to me. He could always scrounge around for 5830s and 5850s, usually ends up costing a bit less per kh/s but also has some drawbacks such as buying used cards (good chance of impending fan death), lower efficiency and less compute density, especially in the case of the 5830.
You aren't kidding about slim pickin's with AMD's GPUs, selling like crazy and hardly depreciating at all.
