Its his personal thoughts talking himself out of buying a Firebolt, it isn't necessarily literal. Breaking the bank is a very common phrase meaning expensive, but not necessarily literal, and Harrys phrase gives off that same vibe to me.
Price on request ... Harry didn’t like to think how much gold the
Firebolt would cost.
He had never wanted anything so much in
his whole life –
Harry is a 13 year old boy, looking at the flashiest toy that exists, say a new 4k TV.
but he had never lost a Quidditch match on his Nimbus Two Thousand,
But he really loves his old 1080pd 120 refresh smart tv.
and what was the point in emptying his Gringotts vault for the
Firebolt, when he had a very good broom already?
Why should i blow my money on something when my TV already works, even though this one is beautiful.
Harry didn’t ask for the price, but he returned, almost every day
after that, just to look at the Firebolt.
Pouts and lusts after that 4k TV hoping it goes on sale, contemplating robbing the store.
Other then that we have the small issue of JKR being bads with mafs. Does she even know how much a broom should cost in her own head related to how much school tuition costs, and Harrys small fortune?
Finally the FireBolt seems to be currently a built on demand product, as in there is 0 surplus and they will only make you one if you pay them enough. They are currently most likely working full time to create enough brooms to supply the pro market, so personal use brooms are still second in production, and can be purchased in advance of public release(if they will ever have one) at a premium price.
‘Irish International Side’s just put in an order for seven of these
beauties!’ the proprietor of the shop told the crowd. ‘And they’re
favourites for the World Cup!’