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Firstly, thanks, and you're welcome!
As to your question, if you're traveling domestically, there is no limit on the amount of cash or equivalents (money orders, bearer bonds, etc. - travelers checks are about to become obsolete) that you are permitted to carry, nor are you obliged to declare it. (International flights are a different matter, where you are legally required to declare any sum over $10,000 that you're traveling with.)
According to the Transportation Security Administration's mission statement, its role is to "protect the Nation’s transportation systems to ensure freedom of movement for people and commerce." TSA Officers (TSOs) are not law enforcement and, in a 2009 policy adjustment, the Administration stated that "screening may not be conducted to detect evidence of crimes unrelated to transportation security" and that "traveling with large amounts of currency is not illegal." Hence, in theory, you should be at liberty to carry as much money as you like on your person, or in your carry-on, and it's the TSA's job to protect you and it, which logically would mean not separating one from the other.
On the other hand, the TSA's Chief Counsel addressed this whole subject in an entry on the Administration's official blog, which seems to contradict the 2009 policy adjustment quoted above:
"Sometimes a TSA officer may ask a passenger who is carrying a large sum of cash to account for the money.
"In reacting to potential security problems or signs of criminal activity, TSA officers are trained to ask questions and assess passenger reactions, including whether a passenger appears to be cooperative and forthcoming in responding.
"TSA officers routinely come across evidence of criminal activity at the airport checkpoint. Examples include evidence of illegal drug trafficking, money laundering, and violations of currency reporting requirements prior to international trips.
"When presented with a passenger carrying a large sum of money through the screening checkpoint, the TSA officer will frequently engage in dialog with the passenger to determine whether a referral to law-enforcement authorities is warranted.
"The TSA officer may consider all circumstances in making the assessment, including the behavior and credibility of the passenger. Thus, a failure to be forthcoming may inform a TSA officer’s decision to call law-enforcement authorities."
In other words, if your cash is spotted, an agent may draw unwanted attention to this fact, and we know of numerous instances of legitimate professional gamblers, with documented evidence of their bankroll and winnings, being questioned at length and, on occasion, having their cash confiscated. Equally or even more disturbingly, there has been more than one instance of TSA agents being convicted of felony theft (see the reader contribution added in the "Update," which is just one such example we've heard of).
So, here are some suggestions:
*Note that while cash isn't detected by the regular carry-on screening devices, the Sentinel II "contraband-detection portal" (walk-through sniffing device) detects even trace amounts of cocaine, methamphetamine, heroin, PCP, THC, and ecstasy and, since up to 75 percent of all cash in Las Vegas is said to be contaminated with one or more of these substances, if the money is on your person and it gets detected by a Sentinel II, that could easily give the TSOs reason to suspect that these are ill-gotten gains, so you may be better off stashing the cash in your carry-on, just in case.