So, I've just noticed that you can play the Tees Valley Line, which as I'm from Redcar has me more than a little interested. Problem is that the game itself is £25, and the DLC is also £25. £50 is a lot of money so I'm wondering if if the Tees Valley DLC is a standalone game or do I need to have the TSW game as well. Probably do, but there's no mention of this on the PS store.
The base game is quite often on sale. When new it was £39, at least for me on PS4. You will def get your moneys worth out of it
I would buy the base game now at £25 and then buy the expansion pack when it eventually and inevitably goes on sale. That way you have not spent two much and get you money's worth with a gap between purchases.