Falling prices in September for plasma televisions and digital cameras sparked the biggest monthly decline in U.S. consumer electronics prices in five months, according to an industry study prepared for Reuters.

A decline of 9.2 percent, or about $250, in prices of 42-inch plasma screen TVs brought their average price to below $2,500 for the first time, and led an overall decline of 2.7 percent for the most popular consumer electronics goods, according to NPD Consumer Electronics Price Watch.

“In September, we saw the first inklings of a plasma price war for Christmas,” said NPD Group analyst Stephen Baker. “There are a lot of these products at $1,999.”

The report, prepared for Reuters and released on Tuesday, showed the price for a market basket of the 27 most popular electronics goods fell to $11,642 in September.

Other flat-panel products’ prices slipped due to growing inventories. NPD said 20-inch LCD TVs fell 3.8 percent to $857, and 17-inch LCD personal computer monitors declined 6 percent to $445.

“Both of these categories benefited from growth in supply and resulting cost declines that have rippled through the supply chain down to the retail buyer,” Baker said.

Prices for digital cameras also fell sharply from August. The average 3-megapixel digital camera now sells for $207, down 6 percent, and may slide below $200 for the holiday season, NPD said.

Prices are already falling for more powerful 5-megapixel cameras, Baker said. He added that consumers may not be enamored of the additional features that the pricey higher-end digital cameras offer.

“(The digital camera market) may begin to look like the PC market, where people just aren’t willing to spend extra money for all this extra stuff they know they don’t need,” he said.

Prices for DVD recorders, 128-megabyte memory cards and digital video cameras also slipped in September.

But a handful of gadgets bucked the declines, posting higher prices in September, NPD said. This group included portable DVD players, which increased 2 percent to $231, and 20-gigabyte hard-drive music players, which rose 2.2 percent to $295.

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