Bottom line lowest cost to learn to fly
Hate to tell you this, but money is what makes airplanes fly - not Bernoulli, not lift/thrust/weight/drag, if there's no money, it isn't getting off the ground, period, full stop, end.
Figure you'll need (guesstimate) 45 hours of airplane time - expect to pay $50 to $55 per hour (that's in the US, expect to pay more - sometimes much more - elsewhere), so you have a minimum of $2,500 in just airplane rental.
Now add an instructor for say, 20 hours, at say $15 an hour (cheap!), there's $300 more, you'll need $300 worth of books, supplies, charts, now you are up to over $3,000, and you better add another $500 for incidentals, surprises, unreimbursed expenses (stopped for fuel and lost the receipt), you will probably want to buy a headset, it does add up.
If you are not doing this "all at once", you'll spend the first 15 minutes of each hour re-learning what you forgot from last time, so now you'll need 50 to 55 hours total time, so the airplane rental portion just went from $2,500 to $3,000.
These are USA prices, and that assumes you already live here and have a place to stay, are eating your meals at home, and driving to a very local air strip. If you need to travel to another country looking for a good price on the flight training, you may spend anything you saved on the costs of living there - you can't camp out on the airstrip.
Two large parts of the $55 per hour rental rate are fuel costs - which are MUCH higher outside of the USA, and maintenance costs - which are also much higher outside of the USA - an awful lot of flight training worldwide is done in Cessna 150s, and that is about as economical an aircraft as you are going to find.
The local weather is a factor, too. If it is good, you can fly most of the time. If it is regularly crappy, you may never get this done.
What I'm telling you is that you will need to accumulate between $4,000 and $5,000 to do this - there really isn't any significantly less expensive way to do it.
Airplanes cost money, and he who rides must pay. Sorry. But it is worth it.
Best Regards,
EchoMike