Probably much less than 20% for a pasta dish with chicken at Olive Garden for example.
The wife and I have started making our own pasta. So a cup of flour, 3 eggs, and half of a Costco pesto container, and we have 2 big plates of fettuccine with pesto.
I'd say that was less than $5 for 2 dinners, with ample portions.
(Obviously no meat in there, but adding something simple like chicken is extremely inexpensive.)
Another plug for Costco BTW... We buy the frozen individually-wrapped fish and chicken there. Pretty much anything you buy "fresh" at the supermarket is previously frozen, so I'd rather buy it frozen and defrost it under my own conditions. I think we get salmon about $25/3lb, mahi about $27/3lb, cod about $18/3lb, and I don't know what the chicken costs but my special needs son has become a chicken aficionado, so the ability to just pull out and defrost a single chicken breast for him is SO easy. But on weeknights, the wife and I can just defrost some fish, throw together dinner with some vegetables, and it's easy and quick.
For those of you who say you don't like to cook, things like this are easy, delicious, and inexpensive relative to eating out.