I'd like to see if we can move to a cheaper package as we need to manage our budget.
If I understand you right, you are only considering metered package from BT (25 GB I think)? Are you not considering other suppliers?
Because, as several people have already said, there are offers from other suppliers for unlimited broadband that are cheaper than BT's metered one.
If you are worried about upfront/set-up costs, I suggest you look at TalkTalk and Plusnet, as they are both offering free setup at present. Sky are asking for £20 setup, but this is offset by their current offer of broadband at £15/month which is unbeatable, frankly - such price wasn't around since 2011.