For bills, there is too much to guess, need to ask:
    frequency:
        then I could work out growth rate



MUCH LONGER/HARDER:
    potentially for each bill_type, there are unique extras - e.g. THIS feels too hard:
        water has 2 fixed charges (water & sewerage) and then a consumption charge (per ML)
        elec has 1 fixe charge (daily) and then consumption (per kwh) BUT, also daily solar rate
        gas has fixed charge and consumption
        internet, kayo is monthly fixed (but can go up sometimes)
        eweka is annual fixed
        phone is messier again.