I’m also outside the M25, and my season ticket with tube would be about three grand, too.
I ditched the tube bit of the season ticket and bought a Brompton. Tube season from Wimbledon to Ravenscourt Park near Hammersmith was about a grand. Brompton was £750 two years ago. It’s quicker than the tube, I get about 90ish miles in a week, and I can also stuff my face. Helps if you have a shower at work – we do, so I get more time with the udderlets in the morning, too.