This can be really good for your budget (even if you only have a few meatless meals a month), because many meat substitutions are inexpensive. I do not buy the "fake" meat products, because when I choose to avoid meat, I want to avoid it completely and not just switch to fake meat products. Instead, I make dishes that aren't dependent on meat.
The one downside, is that the rest of my family are very dedicated omnivores. When my husband hears that I have planned meatless meals, he throws some bacon in the cart ;) So I have to balance what I make so that everyone is happy. When I make meat, I make sure to make myself something else (either leftovers or filling side dishes).
How do you make different diets work in your household?