Is there a way to chart historical consumptions per half hour?

[LampyDave]

My apologies if this is 'simple' or if I've been searching for the wrong terms. I still identify as 'new to this' :)
This is not a query specific to this integration (which by the way is excellent!) but it seems like the sort of problem that someone here might have already solved...
I would like to be able to graph consumption cost against rate for my 3 'meters'. I have set ApexCharts up to extract the information from the attributes of the 'previous day consumption cost' sensors, but that uses the data-generator option which appears to only work on the last state of the sensor. Therefore I get a graph of the last available 24 hrs of data (which is still useful) but it will go no further back.

The graphs I can currently create (along with one at bottom right which shows the daily cost / gain for each meter as well as a total energy cost for the last few days - total cost sensor created and calculated as a helper):

I would like to be able to create these 'per half hour' graphs for historical usage (even if historical means from now on), but think that a) ApexCharts will only interrogate the last available state and that b) in any case the attribute data is probably only kept for 10 days (I don't know how to search for old attribute data so can't check).

The only way I can think to achieve this at the moment would be to make a load of helper sensors which would then need parsing from the Octopus Energy sensors when they update. Seems possible, but also seems like the sort of thing that I might get quite wrong...

Many thanks for any hints if anyone has done this before and has advice. Best, Dave