Note that the cost of a no-fly zone over Syria does NOT include the possibility that the U.S. would not be the primary enforcer.  The U.S. did not have a high participation in the Lilian situation.  Of course, this would be dependent on convincing the UN and other nations to take the lead.

"Pentagon Lays Out Options for U.S. Military Effort in Syria" by MARK LANDLER and THOM SHANKER, New York Times 7/22/2013

Excerpt

The Pentagon has provided Congress with its first detailed list of military options to stem the bloody civil war in Syria, suggesting that a campaign to tilt the balance from President Bashar al-Assad to the opposition would be a vast undertaking, costing billions of dollars, and could backfire on the United States.

The list of options — laid out in a letter from the chairman of the Joint Chiefs of Staff, Gen. Martin E. Dempsey, to the chairman of the Senate Armed Services Committee, Carl Levin of Michigan — was the first time the military has explicitly described what it sees as the formidable challenge of intervening in the war.

It came as the White House, which has limited its military involvement to supplying the rebels with small arms and other weaponry, has begun implicitly acknowledging that Mr. Assad may not be forced out of power anytime soon.

The options, which range from training opposition troops to conducting airstrikes and enforcing a no-fly zone over Syria, are not new.  But General Dempsey provided details about the logistics and the costs of each.  He noted that long-range strikes on the Syrian government’s military targets would require “hundreds of aircraft, ships, submarines and other enablers,” and cost “in the billions.”

General Dempsey, the nation’s highest-ranking military officer, provided the unclassified, three-page letter at the request of Mr. Levin, a Democrat, after testifying last week that he believed it was likely that Mr. Assad would be in power a year from now.

On that day, the White House began publicly hedging its bets about Mr. Assad.  After saying for nearly two years that Mr. Assad’s days were numbered, the press secretary, Jay Carney, said, “While there are shifts in momentum on the battlefield, Bashar al-Assad, in our view, will never rule all of Syria again.”

Those last four words represent a subtle but significant shift in the White House’s wording: an implicit acknowledgment that after recent gains by the government’s forces against an increasingly chaotic opposition, Mr. Assad now seems likely to cling to power for the foreseeable future, if only over a rump portion of a divided Syria.

That prospect has angered advocates of intervention, including Senator John McCain, Republican of Arizona, who had a testy exchange with General Dempsey when the general testified before the Armed Services Committee about why the administration was not doing more to help the rebels.  The plan to supply the rebels with small arms and other weaponry is being run as a covert operation by the Central Intelligence Agency, and General Dempsey made no mention of it in his letter.

On Monday, Representative Mike Rogers, a Michigan Republican who heads the House Intelligence Committee, said that despite “very strong concerns about the strength of the administration’s plans in Syria and its chances for success,” the panel had reached a consensus to move ahead with the White House’s strategy, without specifically mentioning the covert arms program.  Senate Intelligence Committee officials said last week that they had reached a similar position.