Why were the Weasleys poor?

[Catlady (Rita Prince Winston)]

--- In HPFGU-OTChatter at yahoogroups.com, "Wolfie!" <wuff at ...> wrote:
> 
> Yeah but what does a wizarding family pay out in bills?
> They don't use electricity or gas or fuel... so unless water
> and council rates are high, that only leaves a food bill.

I doubt they pay for water (I think it is teleported to them by magic
rather than pumped to them in pipes) or Muggle taxes (council rates),
but they do need clothing, and apparently, even tho' Mrs. Weasley
knits and crochets, she doesn't sew, or whatever the magic version of
sewing is. (I am very troubled by the scene in Madam Malkin's shop in
PS/SS, where she pins up the hem of Harry's robe in the Muggle way --
why can't she just point a wand at it and say Hemmus Pinnus? Better
yet, Hemmus Sewus!)

Floo powder apparently costs money (CoS: "We're running low, Arthur,"
she sighed. "We'll have to buy some more today...."). I have no idea
if there is a monthly fee for being connected to the Floo Network.

We don't know anything about the prices of wizarding health care. 

Nor whether the mortgage on The Burrow is paid off.

I suspect that Ministry salaries are intended to ensure that only
people with an inheritance to live on take jobs there, based on page
ix of Fantastic Beasts: "I was then but a lowly Ministry of Magic
employee ... my pitiful salary of two Sickles a week...."