The base package is 50Gb / month. If you go with Vodafone, 50Gb/month is £30 (was £25 over Christmas) and you can pay a few extra quid and exclude all Facebook, Youtube, WhatsApp, Netflix, Amazon Video, Google Play etc. (i.e. all the big-name sites) from such data usage.
To be honest, I have a steam account with 1000 games. I don't pull anywhere NEAR that as you just can't play that amount of huge games that quickly and keep them all up-to-date.
Sure, you have to be on the right package, but the right package can be £20 a month if you buy a year's contract and buy it at the right time.
Sorry, but with install charges, line rental, etc. any home broadband is significantly more expensive and there are fixed-line ISP's out there giving you less than 50Gb a month without any possibility of exclusions!