Is that flange just the bolt hole broken????? Or is the "pipe" broken..........
If it's solid and it's just the busted bolt hole here's a good fix:
Fix-A-Flange......By Fernco..........is a small cresent shaped metal piece that replaces the bolt hole of the flange..........
It slips under the broken flange to hold the toilet mounting bolt to the flange.......You may need to chip a few tiles to get the fitting under the exising flange............
http://www.fernco.com/noframes/spanner.html
If the whole thing is rusty/broken another fix could be a galvanized bay flange......I've seen other repair flanges too...........