Italy in general was the most expensive Country I visited. Be aware that there are city taxes anywhere between 50 Eurocents and 4 Euro per night that is not included in accomodation charges.
Insider Tip:The view at Michaelangelo plaza is worth the hike to get there (also don't miss the church a little further up). Don't bother with Boboli gardens or the Fort (not worth the cost of entry in my opinion).
Even if you only have a few days in Florence, make sure to do a trip out into the Tuscan countryside (so beautiful and peaceful and can be cheaper than you'd think).
Also, go to the leather markets, but be aware, there's a lot of fake leather out there. The fire test is also a MYTH! Trust your smell!!!