Come and join the dark side!! I've been vegetarian for a month and so far I don't think I have lost any muscle mass... Some of my daily, affordable vegetarian sources of protein include brown rice, wholemeal breads, peanut butter, tempeh, tofu, red beans, etc. I'm not vegan and I do consume some animal products though. I'm taking ON whey protein and 5 boiled eggs a day for some added protein.

The only downside is they tend to taste bland but I haven't controlled my diet for the past 20+ years so it's time for me to eat like an adult.