PHOENIX -- Rosi Freeman and her daughter have a routine during their weekly grocery store runs, but in the last year that routine has become more expensive.

"I would say in the past year they've gone up," Freeman said. "My bill has gone up at least 30 percent."

CHECK: Food Price Increases

Freeman is not alone. The cost of 16 basic grocery items is pegged at $57.46, up 5.6 percent or $3.07 from the second quarter of 2008, according to the latest Arizona Farm Bureau Federation Marketbasket Survey.

Of the 16 items surveyed in Arizona, 11 increased, four decreased and one kept the same average price compared to the 2008 second-quarter survey.

Russett potatoes and cheddar cheese showed the largest retail price increases. A 5-pound bag of potatoes was up $1.24 to $3.39, and a pound of cheddar cheese rose 80 cents to $5.59.

"Acreage planted to potatoes was down nearly 8 percent this year," said Jim Sartwell, an American Farm Bureau economist. "The combination of smaller crop and some production losses in the field has led to higher-priced spuds in the produce aisle."

Matt Croucher, an economist at Arizona State University, said increased demand, gas prices and ethanol production play a role in rising grocery prices, but investors looking for the next market to manipulate are having an effect on the prices shoppers pay for food.

"Of all of the trade volume, only 3 percent is actually delivered so this is just people buying and selling contracts to try to manipulate the price to make a higher profit," Croucher said. "That's really what is what's manipulating the price."

Freeman said she is starting to be more selective. "Even the produce has gone up," Freeman said. "Apples used to be $1.39. Now they're going for $2 a pound."

Economists pass along these tips:

Shop alone.

Take a list and stick to it.

Use coupons.

Buy in bulk, but don't buy more than you can eat.

Buy more "fresh" and fewer "processed" items.

Shop the edges of the store and avoid items at the ends of the aisles.

Use your club card and compare prices.

On the positive side, in Arizona, eggs showed the greatest decrease in price, down 74 cents to $2.25 per dozen; bacon and Cheerios were both down 10 cents to $3.89 a pound and $3.15 for a 8.9 ounce box respectively, and white bread was down 7 cents to $1.59 for a 20-ounce loaf.