Commuting to London.

What is the cheapest solution to commute from Bishop's Stortford to London (Liverpool Street Station)? I have seen on the national railway website that the monthly season ticket costs about 285 £ (no first class and no-tube extension). Assuming that all the people that commute to London are not so rich as surely someone can be. My question is....how is it possible?

Thank you in advance.

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