My sister is 10 years older than me and emigrated to Canada when she was 18. She married at 21 and we went out for the wedding. As is the tradition there, the bridesmaids and also the family held bridal showers. They were fun and part of their tradition, but they were both hosted by others (her in-laws for one and the chief bridesmaid for the other). The idea was a fun afternoon to toast the bride to be and give small gifts. At the same time, the hosts provided food and entertainment, so the only actual cost was the small gift.
To me, if the mum-to-be is happy to have a baby shower, that is her choice. However, it should be organised at somebody's house (or local village hall type venue). Also, food should be provided by all - depending on numbers, it is easy to put a small buffet type meal together for £10 per head or each person can bring a dish. The idea of contributing to a specific gift is fine, but only if people are happy to do so, there should be no pressure on how much to contribute and if somebody wishes to do their own thing, that should also be fine. With increasing household costs, £70 would go a long way to paying for the weekly food shop for my family of 5 and I just couldn't justify spending that sort of money on a baby shower unless it was my best friend and, even then, I would prefer to spend my time making a gorgeous handmade gift.
As for the poster stating how much a day out costs - it all depends on how organised you are. Last weekend we went to visit my eldest daughter and walked to the Cutty Sark in Greenwich. Parking at my daughter's flat was free and we had taken a picnic up for 6 adults - we cheated and bought easy snacks but the whole lunch - rolls with fillings, pork pies, sausages, crisps, tomatoes, fruit and cake bites cost less than £30 for all of us and we had water and drinks from our fridge. When my four children were growing up, it was definitely a case of trying to make use of offers etc for the cheapest possible days out. I worked as a childminder and I took 6 children (3 of my own and three minded children) for a day at the zoo. The entrance fee was paid for using Tesco vouchers and I took a picnic for lunch. As we were leaving, we passed an ice-cream stall - it sold ice creams such as Smartie Ice-creams through to Magnums. The prices were horrendous and so I gave the children a choice - either one of the two cheapest ice-creams at the zoo or back to mine for their choice of ice-cream in my freezer (a large range from Iceland at competitive prices). Fortunately, all except one child opted to wait to get home so money wasn't wasted.
OP - I wouldn't let yourself be pressured into contributing more than you can afford for a gift and I would certainly ask whether anyone could give you a lift to the station so the cost to get home is considerably less. In the current climate, I would hope that the others would be understanding of others financial restrictions.