The mail-in rebates, good through the end of the year, slash $300 off the 450-MHz version and $500 off the 500-MHz PowerMac.
Apple began offering rebates in October, cutting $200 off its PowerBook line of notebooks and $300 off the PowerMac G4 Cube when purchased with an Apple monitor. Those rebates are also good through the end of the year.
The company has used the reductions to try to spur demand after the most recent quarter's sales fell well short of expectations. Apple attributed about $30 million of its sales shortfall to the sluggish sales of the dual-processor PowerMacs.
Apple introduced the dual-processor PowerMacs at Macworld in July, saying that purchasers would get two brains for the price of one.
At the time, analysts questioned the value of adding a second processor, which is not fully utilized by the current operating system, OS 9. Consumers apparently agreed, with Apple chief executive Steve Jobs noting in the company's earnings conference call last month that many buyers opted for the lone single-processor PowerMac rather than the pricier dual-chip models.
With the rebates, the 450-MHz PowerMac now sells for $2,199 and the 500-MHz version for $2,999.