Filet-O-Fish sandwich information: http://www.mcdonalds.c
Promotion is not advertised online because promotional price may vary regionally.
You can check your local McDonald's for their promotional price. For example, in Dunbar, WV: http://www.mcstate.com/24882/40248/2558/
Must be enjoyed with this: song
In the St. Louis area (at least North County) the deal is buy a Filet-O-Fish & get a second sandwich for $1.