I grew up a working-class Tory - my parents used to vote Labour, but voted for Thatcher.
The Tories believe in giving you the freedom to make your own choices. They believe in taking responsibility for yourself, your family, and those around you. They won't casually throw away taxes (and worse, debt) so people can realistically view benefits as a lifestyle choice. They believe that the State is the servant of the people; not its master.
The Tories (again in theory) won't run up huge debts. They will cut your tax (again in theory). They will always have to come in to fix Labour's mess - because every Labour government in history has left the national accounts in a disaster zone. They will cut bureaucracy, and tell the EU to piss off. They care about our military. They don't want low-skilled immigrants coming to Britain.
These aren't concerns only for the rich.
Above all, though, they stand for aspiration.
Thatcher taught the country this, more than any other Tory PM. She showed us that it was possible for the ordinary working family to fulfil their dreams and make a better life for their children, without relying on the State. Before her the idea that ordinary people could afford cars or foreign holidays was ludicrous. Yet by the end of her time, hundreds of thousands had bought their council houses, and even owned their own shares in the newly privatised industries.
Not many people earn £50000 a year, but working-class Tories believe it is at least possible for them. If not for them, then at least for their children, if they are given the chances to make the most of their abilities. Clever but poor kids had the chance to escape poverty in grammar schools.
Sadly, though, the premise of the question isn't entirely empty. As I have said here dozens of times now, this is Cameron's biggest weakness. Unless he gets the "strivers" on-side, like Mrs Thatcher did, he won't be able to win a majority next time around. He just doesn't "get" aspiration as instinctively as Thatcher did. He is a little too metropolitan and urbane to automatically click with these voters. Part of it, sadly, is background - he can't do anything about that though. Everyone could identify understand a grocer's daughter, even if they didn't like her ideas.
Thankfully, though, Cameron just has to be better than Red Ed - who, just like the OP, doesn't "get" why people might vote Tory. That is already a huge disadvantage.