I'm going to go out on a limb and say that you've already answered your own question.
How much money does the family have in Book 3?
The 700 Galleons that Mr Weasley won is equivalent to approximately £3500 (about $5500). Even if they spent 90% of this windfall on their trip to Egypt, that would still leave the family with seventy Galleons.
Obviously seven of these galleons would be needed to buy Ron a new wand (since we know that all wands cost 7 Galleons) but that still leaves the family with 63 Galleons (£300) to spread out among the family over the following year.
How much does Ron actually spend in Hogsmeade?
First Trip
It's not clear. On his first trip, he and Hermione promise to buy Harry some sweets. They evidently had a Butterbeer and various free samples of fudge. On his return;
A shower of brilliantly coloured sweets fell into Harry’s lap.
But it's not clear whether he paid for any of this or, (far more likely) whether Harry gave him the money to buy him some sweets since he wasn't able to go himself.
Second Trip onwards
The same is true of pretty much every subsequent trip. Either Harry or Hermione isare with him at all times. We don't see him spending his own money other than buying family presents or small one-off purchases like Butterbeer (two Sickles).