Why does Walt sell the Aztek for a mere $50?

Missed in my question as well as from my memory was a character of significance. A character whose presence precipitates in Walter giving away his reliable Aztek. The character is Walt's porkpie hat!

Just as the mechanic says that the Aztek is good to go for at least another 200,000 miles, Walt has a sense of foreboding that he isn't going to be around to drive it another 200,000 miles. At the very next instance he looks at his new hat (which IMO is a clever device to fadeout Walt's old persona and introduce this new fearless Walt) and is reminded that the Aztek is a reminiscent of his old life. A life where he was afraid of people like Gus and Tuco. But no more he considers himself in danger, and rather considers himself the danger.

Thus, him selling his car for such a ridiculous amount is the action of kicking away his old lifestyle and buying himself a new one (the Chrysler 300). Somehow, now he has become reckless with his decisions and doesn't consider any problem too big for Heisenberg to overcome. This and the swagger that comes with becoming filthy rich leads him to "selling" off the old car and getting a new one.

P.S. These sources: 1 and 2 further elucidate the point.

At this point in the show, Walt makes more money than he could possibly safely unload. He must find ways to dispose of the funds beyond simply setting the cash on fire.

With that in mind, dropping his current car for only $50 makes fiscal sense. I believe the Aztec is currently owned by Walter, making it an asset and therefore adds to the current overflow of cash he has. By getting rid of it, he is no longer fiscally accountable for the car.

Walt Jr., who has no experience buying or selling cars, wouldn't know to question his father's actions, and having been given a new car, he is too excited to care.

The buyer of the older car for $50 would apparently rather take the presumably unethical deal quietly and get a great car for practically no money.

By leasing the two new cars instead of owning them, Walt presumably spends more money than he would buying the cars. Leasing is usually a more expensive proposition than buying a car outright, and after a lease ends, it does not result in you owning the car. Leasing these cars creates a financial drain, which Walt needs.

Considering his financial and legal state, Walter made good business decisions here. Also it's his birthday and he presumably freed himself from a horrible situation; he's rewarding himself for a job well done.

I saw it as a bit if irony on Walt's part for several reasons.

1) He really didn't need the money that would have come from selling the car. He had more than enough cash to buy any car he wanted, several times over.

2) As was later revealed, part of why he was in his station as a teacher, underappreciated and struggling financially, was due to a fallout between him and his partners in the company they founded decades earlier, referred to as Gray Matter. Walt informs Jesse that he sold his stake in the company for a paltry $5000, "A few months rent," as he referred to it. Then the company became a huge, multi-billion dollar entity, of which he had no stake or claim to. He sold his and his family's future for a few grand and petty reasons, when he could have been a millionare had he simply reconciled his differences with the founders. Now he has more money than he knows what to do with, so selling the car for a paltry sum is likely Walter having a moment of irony in his new life as a drug lord: he cast off one life he could have had for a small amount of money, why not do it again?

What I took from this scene:

• Walt wants a better car
• He doesn't care how much he gets for the Aztec because he doesn't need the money
• The Aztec reminds him of his previous life as a loser
• It's also fairly distinctive. It's probably best for Walt not to be recognised by the car he drives
• It's a horrible, ugly car
• He might not want to deal with the paperwork involved in formally transferring the car to the mechanic, so offers a ridiculously cheap deal to tempt the mechanic to do it 'off the books'
• To impress Walt Jr.

Walt hates Aztec. That's the kind of car Walt had to drive and not the kind of car Walt wanted to drive. It embodies dullness, practicality, prudence and lack of ambition of pre-Heisenberg days, it's the vegetarian bacon of the car world that we witness Walt consuming without much enthusiasm. It's Skyler's choice.

Aztec was a flop in sales and evidently Whites family bought the car from brand new with a huge discount, based on the attractive price, reliability and practicality. Walter never liked the car. We get a peek into his real passion for driving in the later episode when he empathises with Walt Jr. desire to get Charger and then goes into fiery doughnut painting session once told by Skyler to take the Charger back.

Still 200,000 miles left? That's 10-20 years of uninspiring, lifeless motoring, the prudent much hated choice?

As we know Walt has uncanny ability to add up numbers in his head. My guess is that Walt quickly does miles-into-years conversion and 10 years until the car change seems like a very long term to a man whose life was hanging on a shoestring for a year. Why not do it now then?

Walt acts with the resolve and urgency of a person who had a near death experience and arrogance of his belief that there are no more predators that can match him in this new situation.

$50 is a token payment; Charger for Junior? What the heck, it's just like a new pair of boots.

All the "leasing" talk is aimed to soothe Skyler, Heisenberg doesn't really care that much at this stage how he is going to explain the purchase to others. He just knows that somehow he will.