Taking an approach means selecting the direction from where you want to start solving a problem.
For instance, I could find myself wanting to teach someone a language.
I could start with just vocabulary, or I could start with grammar.
Those options could be described as a "vocabulary-first approach" or a " grammar-first approach".
Approach comes from the verb approach which means moving closer to a goal. When there are several directions from where to reach that goal, I have the choice of several approaches.
The word is also used in a more literal sense, for instance when an air plane is going to land, it approaches the airport. When it is lined up with the landing strip, and it descends to actually land, we say it is on final approach.
A moment in time can also approach: the end of the month is approaching as I write this.
In your sentence, the word is used in a figurative way. There are supposedly several ways to accomplish what you want to accomplish, and most books take a specific direction to get there.
A better definition of "got off easy" would be "without much hardship or cost". That can mean that you didn't get punished very severely, but in this context it means that whomever was speaking got a good deal on the Quidditch World Cup tickets they bought.
The phrase "got off easy" has the connotation that the usual consequence or cost is much more unpleasant or costly than the actual consequence/price in this situation. The tickets could have cost a lot more, but he "got off easy" with a lower price.
Some examples:
She might have gone to jail for a long time, but got off easy with just community service.
I could have ended up in the hospital, but because I was driving slowly I got off easy with just bumps and bruises.
I didn’t know it at the time, but apparently, I got off easy. When my best friend from college got married last summer, I had to spend only $1,000 total for her bachelorette party in Las Vegas, my plane ticket from New York to Los Angeles, hotel room, bridesmaid’s dress, shoes, hair styling and wedding gift.
(Source: HuffPost)
Best Answer
Take off means:
(Cambridge online dictionary)
The sentence means that because batteries are now cheaper and can store more power, more people might want to buy of battery-powered vehicles, so the sales of these vehicles would grow considerably.