M&S have a standardised pricing policy, so station/airport outlets are no more expensive than high street, which actually makes them very reasonable along with the quality you expect from M&S.
The generically branded Cider is actually made by Westons, not sure what the beers are but it's all decent stuff.
They've been my first choice for years when the other options are very expensive station shops.
The M&S at Liverpool Lime Street charges £1.09 for 1 can of that cider, or £3.95 for 4.
I like their range of canned craft beers. Some of them are brewed by Fourpure (London).
The bottles of M&S "Citra" are £2.65 for a 500ml bottle and are actually brewed by Oakham, and is in fact a bottle conditioned and stronger version of the wonderful Oakham Citra that most decent real ale pubs have on from time to time!
There's also a Sainsbury's Local opposite Lime St station. Decent prices on 4 packs of lager and cider, and you can also pick up bottles of Sainsbury's brand "Porter" (can't remember who brews it) for £1.60. Badgers "Blandford Flyer" and a few others can be had for £1.60 - £1.85.
There's a Tesco Metro down on Clayton Square with an even bigger choice if you have more time.
And you've also got the North Western 'spoons at Lime Street station; but expect a very long wait to get served at the bar. It's quicker to walk over to the Richard J Blacker 'spoons across the road!
