"I could rent a cheap hostel and find cheap food, but airfares were always the biggest barrier."
Since then, the London-based American, from Texas, has visited more than 43 countries in three years by taking advantage of the lowest fares online.
The cheap deals that he finds he shares with his subscribers, with some paying £35 ($65) a year to sign up to the service, which has since netted him £750,000 ($1.4m) in membership fees.
Last year, Mr Sheldon took to Reddit to share his advice, and it proved so popular it crashed the inbox of his subscription service and swelled its membership to 200,000 savvy bargain hunters.
Here we reveal some of the tips that caused the meltdown...
Set alerts for destinations and be flexible
If you're interested in a route, Jack advises that you set up a Google alert and be open to a number of dates you could potentially fly.
He advised: "Put in particular dates and then you should see a button/switch that says 'Track prices'. Enter and track a few different dates for best results."
He added: "Set an email alert for price changes on those dates. If you are flexible, I would enter ten different dates and set an alert for each one.
"Try a vague search by continent on Google flights. Change the month of travel and see if anything strikes you as interesting."
Do your research
"Once you find a cheap fare on Google there are a number of other places to look to make sure its genuinely the best deal.
"Momondo picks up fares from the cheapest agents.
"Another option for those that are very flexible with the amount of stop-overs is lesser-known kiwi.com. They search a lot more options for each route than even Google and Skyscanner does.
"The deals I send out tend to be a max of one stop unless it's a vastly discounted fare on a two-stop long-haul."
He said he also highly recommends the fare alerts on Skyscanner and has around a thousand of them set up.
Look for mistakes
Occasionally computer glitches can throw out shockingly cheap fares which some airlines choose to honour. However Jack recommends waiting a week before booking your accommodation as a carrier may be able to renege on the booking in this time.
Jack revealed: 'The best I've seen has been an £18 ($33) mistake fare to Belize. The best I've taken has been a £112 ($208) single stop round trip fare to Bali.
"It's a special feeling walking onto a flight knowing most everyone else paid five to eight times more than my fare."
Jack's website finds mistakes and cheap tickets and sends them out to subscribers. One deal included Manchester to Boston for £200 ($373) and London to Tokyo for £272 ($507).
Use local sites
Jack said: "If you're booking with a foreign airline, always log into their local sites to see if you can get a cheaper price that way.
"They often will offer lower prices for locals, but it is perfectly legal to book using that method."
He recommends a VPN (Virtual Private Network) connection when looking at local sites such as TunnelBear, which has a chrome extension.
Book direct
Although Jack checks first if he can save money booking through an agent, he only opts to do so if the saving is more than £50 ($90).
"Depending on how often your travel plans change, it may make more sense to always book directly with an airline."
Find the booking sweet spot
Jack says: "Last-minute deals aren't going to be very common as airlines try their best to take advantage of business travellers and hike up their last-minute rates.
"Six to 12 weeks in advance is the sweet spot, but it varies greatly.
"For peak and holiday seasons, I recommend looking just as the flights start showing up (typically 11-12 months in advance)."
