An insightful article this week from the Atlanta Journal-Constitution this week chronicled the rock-and-a-hard-place challenge of restaurant companies right now. On one hand, weak consumer spending and high unemployment has prompted most casual dining and fast-food chains to slash prices to keep customers at the table. On the other, inflating agricultural commodity prices mean produce, grains and beef are getting more expensive by the day.

That means the big question for 2011 is not whether restaurants will pass those prices on to consumers, but when and how much. And the lowest-priced items on the menu are natural targets since margins are already razor thin in most cases.

In short: The Dollar Menu at McDonald’s may have to find a new name in 2011.

To be clear, McDonald’s (NYSE: MCD) isn’t tossing out the menu just yet or dramatically jacking up Big Mac prices nationwide. But the writing is on the wall.

Just several weeks ago, the company admitted McDonald’s menu prices may rise if the crunch in prices gets too severe. McDonald’s predicts commodity prices will jump 2% or 3% in 2011 and claims that’s a fairly manageable number. But that range is simply an estimate, and reality could be quite different. Consider that crude oil has just crested $90 a barrel, pushing gas prices above $3 nationwide for the first time since 2008. And it’s not the only commodity soaring — copper prices are up 30% this year, cotton prices have doubled this year and are approaching 15-year highs, and everyone knows that precious metals like gold and silver are on a tear.

Oh yeah, and the price of wholesale choice beef

is up 15% in 2010.

On top of real price inflation outstripping estimates, buried in the recent Journal-Constitution article is a telling revelation from McDonald’s officials that “menu prices could rise if the economy improves.” In short, the only reason they haven’t hiked prices already to offset rising costs is because spending is seen as too fragile and MCD doesn’t want to scare off customers. Once spending firms up, so will prices.

I don’t mean to single out McDonald’s or paint the company as the bad guy here. The bottom line is the bottom line, and margins are simply unsustainable for many restaurants – indeed for many businesses across all sectors. According to the Philadelphia Fed’s Business Outlook survey for December, “input prices” are spiraling upwards for just about everyone. Specifically, “52% of firms surveyed reported higher prices for inputs, compared with 38% in the previous month.” And that 38% in November was up from 34% seeing higher prices in October. And that 34% was up 23% in September. You get the picture.

But McDonald’s has a unique problem that chemical companies and automakers don’t have to deal with – it has a Dollar Menu, a list of items with a firm ceiling on price dictated by the very name that list carries. That leaves little relief to offset costs.

Which means one of two things could disappear in 2011 – either the Dollar Menu moniker, or what’s left of McDonald’s margins.

Jeff Reeves is editor of InvestorPlace.com. As of this writing, he did not own a position in any of the stocks named here. Follow him on Twitter at http://twitter.com/JeffReevesIP