Use a moon cup (organicup) which is fine with heavy periods as long as you empty it often enough.
Mine has capacity of a bit over 15ml, and needs changing every two hours or less on the heaviest day, else it does overflow, so I also use pads then.
Prescription cost for Tranexamic acid is £9, though not every month.
More toilet roll, more laundry.
I agree a lot of period poverty is caused by neglect, by girls who don't have the confidence to tell parents they need supplies, and by financial abuse to partners, spouses, children, so some women simply won't have the money available to them. Not to mention actual poverty.
You might not have transport, so only have access to a more expensive local shop with less of a range of options, rather than a big supermarket with own-brand options as well as cheaper branded supplies.
If you are in temporary accommodation through poverty, you may not be able to afford the upfront costs of reusable or a menstrual cup. You may also not have access to facilities to be able to sterilise a mooncups, nor wash reusable pads. (Or reusable nappies, if you have a baby.)
If you're budgeting to the point that you're deciding between a loaf of bread or tin of beans to last you the rest of the week, you're probably not going to prioritise sanpro.
You might go to the GP to help manage your periods, and maybe they prescribe something to stop you throwing up and painkillers which aren't available over the counter. If you're that poor, you'LL probably be eligible for free prescriptions - but it does assume you are literate and sufficiently together to complete the relevant form and send it off, and not to have moved on to other temporary accommodation before you receive an exemption certificate back.
Still, on the bright side, if you are sufficiently under-nourished, your periods will probably stop.