Dangerously low on petrol and food, they waited for the funds to be transferred. The children sat at a foodcourt and waited as their parents tried in vain to access the money at their bank branch.
The family eventually scrounged for loose change in their pockets and in the used station wagon they had bought in the US for the trip. They had spent $8,000 on the car and the camper trailer, in which they slept at night when they were not staying with friends.
They rustled up enough to buy a loaf of bread, which they ate with leftovers: ham, soggy lettuce and Cheerios, a breakfast cereal. Later that day, Mr Ong tried his luck again at a petrol kiosk and, unexpectedly, the card cleared his request to buy petrol.
They drove to their next destination, Casper, Wyoming, where they stopped for the night at a campsite and Mrs Ong cooked instant noodles.
She says: "We never imagined how a trip could change our lives. When you do a trip like this, you put yourself out there, you make yourself vulnerable. We met new people, which opened up new opportunities. If you planned everything to the letter, you might miss out on something."
Besides Americans who welcomed them into their homes, many Singaporeans in the US contacted the family to arrange to meet. A Singaporean they met at a barbecue, organised by another Singaporean, was working at Pixar and gave the family free tickets to Disneyland, worth about $1,000.
Mrs Ong had told the children they were not going to Disneyland as they could not afford it.
Having a tight budget meant "we lived like vagabonds for six months", says Mrs Ong.
The family mostly visited free attractions such as museums and monuments. They did not have much cash for souvenirs, although Mrs Ong bought 108 fridge magnets to commemorate their trip.
They spent prudently, for instance, investing in a family pass to the national parks for US$80 (S$115). Besides visiting attractions such as the Statue of Liberty, they saw 20 of about 60 national parks in the country, including Yellowstone National Park.
They often slept in their camper, which the boys and Mr Ong set up when it was time for bed.
The camper covering, made of canvas, meant they had to put up with temperatures of between 10 and 40 deg C.
On several occasions, there was no campsite available, so they spent the night at a Walmart carpark, sleeping in the car as they were not allowed to open up campers, says Mrs Ong, who learnt to wash her hair in public toilets.
"You learn to adapt. We're resilient," says Asher.
Around the US on a tight budget
Mrs Sue Ong's tips on taking a long trip in the United States with a big family on a small budget:
• Buy an old but well-maintained car. They are affordable by Singapore standards. At the end of the trip, you can sell it and recoup some of the costs.
• Skip hotels and make your own sleeping arrangements, for example, sleeping in a camper or tents. Camp grounds are affordable and easy to find.
• Skip restaurants. Shop for groceries and cook simple meals. "If you have no opportunity to cook, we found affordable options such as fresh and nutritious submarine sandwiches sold in the larger grocery stores. The large pizzas sold at 7-Eleven stores in the US were also a favourite with our kids," Mrs Ong says.
• Skip tourist attractions that charge fees. "The US is not short on wonderful things to see and do for free. For example, most of the world-class museums in Washington, DC are free of charge to visit," she says.
• Shop at thrift stores. It is not difficult to find them in any American city or town. These stores are typically large and sell just about anything you need, such as clothes (including winter clothing), shoes and kitchen necessities.