The ECS NFORCE4-A939 is out in Japan and it's a really cheap board, about $100. Here's a
pic and here's a
review of the KN1 Extreme, which uses the same PCB but has additional extras.
Based on past nForce3 boards I would say that Gigabyte, Chaintech and EPoX will have boards with very good performance/cost ratio, and ABIT should have something cheap also. The thing is, will they make a cheap nF4 Ultra too? So far that's a yes only for Chaintech.
If you can find the Chaintech for sale go for it, just remember to have some air blowing to the chipset heatsink if you're overclocking.