Even Dean Ornish's diet has 10% of maintenance calories as protein. I would put the low end number at 10-15%, which would perhaps be in the range of 50-75 grams of protein per day (assuming 2000 calories).
You don't even have to have protein every day as long as you average enough. Don't forget the protein content of foods that are not the usual suspects. An avocado has 9 grams! Okay, maybe not a good example in your financial situation...
Eating protein only once or twice per day is fine. I think the minimum dietary requirement for protein is 5% -ish of total intake assuming isocaloric conditions. I think I have a link, I'll go search for it. (If I can find it, I'll post it in the comments for this answer.)
Update: I think I'm deriving the 5% number from the minimum amount of protein required to build muscle in a hypercaloric situation. In isocaloric situations, women and men require approximately 8-9% and 9-10% of total intake respectively. I've also found sources suggesting 0.8g/kg of body weight, which translates to approximately 9% in me personally.