My local Wendy's offers them for $4.39, but I received mine for free courtesy of Wendy's.
I tried one of the mushrooms off the bat and there was a pretty strong mushroom flavor. It mellows out when mixed in with everything else.
Nutritional Info - Wendy's Bacon Portabella Mushroom Melt (219g)
Calories - 660 (from Fat - 350)
Fat - 39g (Saturated Fat - 18g)
Sodium - 1450mg
Carbs - 39g (Sugar - 7g)
Protein - 37g