Some things I'd like to point out though:
Leasing isn't necessarily bad, you just have to know what you're doing. It is much more useful to lease medium-size aircraft, such as the 737 series, because they generally cost less to lease per month (brokers offer it around 1.5 million) and they generate a much higher income than the larger, and more expensive, long-range airplanes.
What I tend to do before wanting to lease an airplane, is take (the leasing fee + X) and divide it by 24, where X equals the average slot cost (€40.000) times the number of routes you can fly with it. This will give you the approximate DOP the airplane has to make to become profitable.
So if I want to lease a 737-400 from my own brokerage (leasing at €850.000), which could be making 7 or 8 flights per day, I calculate the following:
X = 8 * 40.000 = 320.000
(850.000 + 320.000) / 24 = 48.750
So the aircraft will have to make €48.751 per day to be profitable, which is very possible with a 737-400. However, if I decide to lease a 747-400 from another airline at the used market for 12 million, it may seem like a reasonable price, but try to calculate it.
X = 2 * 40.000 = 80.000
(12.000.000 + 80.000) / 24 = 503.333
Now, the aircraft will have to make €503.334 to be profitable, which 1) is much harder, and 2) will give you a much lower return.