There was his plane ticket to the U.S. from Pakistan, as well as a return flight to the United Arab Emirates, at a cost of less than $800 each way. Add to that his living expenses, including three months rent for a Connecticut apartment at a little less than $1,200 per month.
His car bomb was relatively cheap, too: $1,300 for a rusting 1993 Nissan Pathfinder and the cost of some firecrackers and tanks of gasoline and propane.
Shahzad, who seemed to have paid cash for many and maybe all of his purchases, bought himself a Kel-Tec rifle, which sells for around $400, but skimped on luxuries.
The 30-year-old slept on an air mattress in a sparsely furnished apartment, and, according to one account, tried to get a job at a jewelry store where he had worked as a young college student.
Shahzad's finances are under scrutiny, as authorities try to learn whether he got cash from a terror group.
A law enforcement official told The Associated Press on Thursday that investigators had identified and were looking for a person who helped courier money to Shahzad from an overseas source. The official spoke on condition of anonymity because of the sensitivity of the investigation.
Matthew Levitt, a former U.S. Treasury intelligence official, now a senior fellow at The Washington Institute for Near East Policy, said the fact that Shahzad paid for the car and plane ticket in cash, sometimes using $100 bills, was a "red flag."
The money trail, he said, may provide valuable clues as to whether Shahzad had any help.
Yet the bombing plan, as described by authorities, appears to have been simple enough that even a single person or a small group with limited means could stage this sort of attack.
Shahzad's rent from mid-February to the start of May, his two airline tickets, gun and vehicle purchases appear to total less than $7,000. The actual bomb components - fertilizer, propane tanks, and a few boxes of cheap firecrackers - were even cheaper, maybe a few hundred dollars at most.
"You don't need to have a lot of money to put together a bomb.
It's all relative to what you want to make," said Leo W. West, a retired FBI explosives expert. He noted that a more sophisticated device containing exotic chemicals would have been more expensive.
Prosecutors said that on May 1, Shahzad tried to detonate an SUV filled with flammable materials in Times Square. The vehicle smoldered, but didn't explode. He was arrested after investigators traced him through the SUV's previous owner.
Shahzad is in federal custody. Authorities said he is coopering with investigators. He has yet to be arraigned. The whereabouts of his wife and children has not been made public, but they are believed to be living overseas.
Born in Pakistan, Shahzad spent more than a decade in the U.S., going to school, working and starting a family, before moving back to Pakistan last spring.
Shahzad has been characterized as being in money trouble when he left the U.S., but records and interviews suggest he still had resources.
He came from a well-to-do family. In America, he held a steady white-collar job as a budget analyst for years - a job he only gave up when he left the country.
Until that departure, there was no trail of lawsuits or missed payments indicating he was in trouble. In fact, his financial history was clean enough that Wachovia Bank gave him a $65,000 home equity line in January 2009.
Five months later, he left the U.S., stopped paying his mortgage and his home heating oil bill and let the bank initiate foreclosure proceedings, but it is possible that step was made, not out of financial desperation, but because it made economic sense.
As of June 1, 2009, he owed $200,673 on his mortgage, according to court records. That, plus the home equity loan, raised his liability to $265,000 - more than the home's current appraised value.
It was unclear from public records how much of the home equity loan Shahzad used before moving his family to Pakistan, but if he pocketed all $65,000, it meant that by walking away from both loans he could recover most of his investment in the house and leave the country with a nice stake for the future.
Shahzad's financial situation in Pakistan was unclear. Friends and relatives have offered little information on where he and his family lived or how they supported themselves.
His father, Bahar ul-Haq, is a retired vice marshal of Pakistan's air force and owns property in several parts of the country. Shahzad's wife, Huma Mian, also comes from a successful family. Her father, Mohammad Asif Mian, is a petroleum engineering expert who has written several books and technical manuals, worked for energy companies including Saudi Aramco and Qatar General Petroleum, and has two master's degrees from Colorado School of Mines.
Still, when Shahzad initially returned to the U.S. in February, he phoned an old boss at a New Haven jewelry store where he had worked while attending the University of Bridgeport and asked for a sales clerk job.
Sylvia Lee, of Dynasty Jewelry, told the New York Daily News she had to turn him down because business was slow.
Acquaintances continued to express bafflement this week as to why Shahzad might have done it.
"He was a normal guy. Normal guy. Just enjoying life," said Shakeeb Murtaza, who was part of Shahzad's circle of friends when he lived in Connecticut. He said he hadn't been in touch with him since he left.
Nasir Khan, a relative in the family's ancestral village of Mohib Banda in northwest Pakistan, said he remembered Shahzad talking about the problems of Muslims in Iraq and Afghanistan.
He also said Shahzad had become more religious over his time in the U.S., compared to how he was as a boy.
"I saw a little change in him. When he was here, he was not religious-minded. But he was, when he came back from the United States," Khan said.
Col. Abdul Aziz, a close friend of the family who served with Shahzad's father in the air force, called him an "obedient and such a nice boy."
"I am flabbergasted that they say he has done this. Someone must have brainwashed him," he said. He added that he didn't believe the allegation that Shahzad had gone to Pakistan's tribal areas to get terror training, saying it was unlikely he could have traveled there without his father finding out.
"His father would never have given him permission," he said.