London Commuters - cheapest travel options.

Been offered a job at a really great company, which would bring lots a career growth in an industry that's hard to find roles in.

That being said, they've asked I commute 3/4 days a week, I'm based 2.5 hours away from London, they aren't able to cover expenses for travel and the price for trains is crazy. Unsure what to do, is 4 days too many. Any suggestions for a cheaper travel trains/car.

Potentially looking to move closer after 6 months, if I accept.