price of keeping a horse - Any advice appreciated!!

Okay so I'm really looking into buying a horse of my own, I've been riding for 10 years now and I think I might finally be able to make my dream come true!
I was just wondering if anyone could tell me what they pay weekly for their agistment and feed (just an average cost of what it might be). I've had a good look around and i've found some nice looking places for $60 and $30 a week (not including feed). The girl who showed me around one of the places told me that some horses are fine just living off grazing, is that true or is hard feed a better way to go? I live in Adelaide, Australia but any Australian replies are welcome.
Any advice is highly appreciated!

I pay $500 a month for 2 horses (which would be $125/week, which is $62.50/week/horse)

For this price they each have a large stall, are fed twice a day, shavings and hay are included, but I buy my own grain. They are turned out for about 20 hours a day on lush pasture. There is an outdoor riding arena. I generally clean my own stalls, but the owner will clean for me if I ask her to. The owner will also put/on take off blankets/flysheets etc.

It's a small place with only 3 other horses, 2 of which belong to the owner of the place. Very peaceful and drama free.

It all depends what kind of horse you are looking to buy and for what purpose...
If you want a working horse as you say you have been riding along time then you need to weigh up the costs of livery, grazing, feed, tack, transport, and passports etc
Im not sure what the law is in Australia but in England you have to have a passport for your horse to legally sell buy loan or transport a horse. And don't forget the cost of keeping a horse changes via season. If its summer grazing for a horse is ok but then you need to keep an eye on the grass and you will have costs for fly masks, creams and every thing else. ... Then in winter you need rugs, blankets and everything else...
You can find cheap places to buy all of this and then really good second hand places. If you wanna know anything else just ask

Monthly cost after purchase of tack and other things that don't "run out", or are maintenance (food, board, farrier, shots), would be at least 400 USD. Bare minimum! - if it's a bigger, working horse (draft, or just a plain working/showing/training horse) up the cost significantly. This of course is all dependent on the prices where you live.