Broke that down. About 298 non-negotiable cost for students, about $375 in US Dollars for things that can't be transferred, assuming everyone keeps their gloves, cauldrons, scales, phials, and telescopes after school is over, instead of giving them to younger siblings/friends of the family.
674 pounds, or about $850 US Dollars are for things that could be passed down to the next year, for a grand total of about 6000 for every year. Hogwarts costs less than $1,000 dollars a year assuming you buy everything new, you could probably get it significantly cheaper if you're pinching pennies.
12000+2625= 14625 total spent for the Weasley;s to send all of their kids to Hogwarts (assuming books and the like are passed down, and buying two of everything for Fred and George. If they had to share, drops to 575 a year.)
How poor were the Weasley's that they couldn't afford decent stuff? Alternatively, how much did they hate Ron that they couldn't drop fifty bucks for a new wand?
Hell, they probably SAVED money sending their kids to Hogwarts, simply because they didn't need to FEED them for most of the year! Seriously, how do you manage to be poor with freaking magic?! DAMN IT ROWLING! Transfiguration alone takes care of a huge number of basic needs, like furniture, clothes, dishes, and other simple things we use without thinking. Herbology probably has some fast growing fruit plant to feed everyone. Ditto for Magical creatures and Meat/Dairy. Charms fill the role of pretty much every basic machine we have. Potions probably covers basic medicine plus a variety of other effects... Runes, Arithmancy, Astronomy, Divination, Muggle Studies, and History of Magic probably wouldn't affect things too much, though Muggle Studies would probably let them make a killing in business on that side...
Damn, how fucking incompetent are wizards that they manage to fuck shit up so badly that they are poor!?! Damn it Rowling. This is your fault for trying to make the later books more realistic.
Alright, done ranting for the moment. On to other thoughts.
Free tuition means Hogwarts is a public school, meaning that pretty much everyone in attendance is not particularly rich or prestigious.