Vodafone had to pay £378m to buy the right to use the 50Mhz band for their 5G services. (Other operators also had to fork out vast sums of money, with EE, for example, paying £303m to use the 40Mhz band). That's before they could even make a start on building transmitters and putting the infrastructure in place to get their systems up and running.
So a fiver a month, for example, to get unlimited calls and texts (together with 3 GB of data) using the Vodafone network via Asda Mobile's bundles, seems like extremely good value to me!
When I first got a PAYG mobile phone, 22 years ago, I was charged £1 per day as a standing charge. So that was £30 a month gone without even using the thing! Outgoing calls were charged at 50p per minute from the time that the phone at the other end started ringing (with no automatic cut off, as there is now). So making an unanswered call, where the phone was ringing for two minutes, took another £1 from my PAYG credit. Incoming calls (which were often only from spammers and scammers) were charged at 30p per minute too.
In comparison to those prices, today's charges for using mobile phones seem ridiculously cheap to me!