I recently backpacked in Australia for 3 weeks and budgeted $100 AUD a day. It was reasonable, but didn't allow me to do everything I'd like.

A hostel will cost you ~$30 a day, $20 if you find a great deal.

A good meal is hard to find for less than $20. Achievable but difficult. $10 is probably a minimum.

The bar is where your budget gets blown quick. $7 for a pint is pretty typical. $5 is a good deal. You can get half pints or schooners for less, but no better value.

Buying beer at the store, it's still around $2 a bottle for the good stuff, and you won't find any beer for less than $1 a can (30 pack of VB was around $35).

So, bare bones day (with drinking) would be $20 for lodging, $25 for food, and $25 for beer. That's $70 and you haven't done anything else yet! Add travel between cities (even buses cost something) and any fun, and you can get to $100 quickly.

Some days when I didn't drink, I could do a day of making my own food and lounging on the beach and only spend $15, but I was still spending $25 a day on lodging. So you can get to your numbers, but not easily.