Wouldn't be surprised though if the original channel ran on a much tighter budget than the half channel we have today.
Probably difficult to calculate. In those days it was very much a seperate entity. Now its become very much a core service and integrated into the rest of BBC News, I'd imagine it's individual budget is a lot smaller, but overall a lot more
I've had a look at several annual reports from the last 15 years and it's not immediately obvious how it compares due to changes in reporting.
Overall BBC News expenditure is not reported separately. Presently, BBC News channel content costs are broken down as follows: production costs, newsgathering costs, other costs. Presumably radio, nations/regions and programmes such as Newsnight have additional newsgathering costs. And then there's Global News and World Service.
Production costs for BBC News channel/24 were £23.5m in 2015, £30m in 2010 and £23m in 2005. 2000 was £48m but that will include newsgathering costs.