Hotels near Polar Ocean World are relatively expensive, so five people want to eat in 400 yuan anyway. You can walk a little to Hong Kong East Road, where there are residential areas and Qingdao University, and there are some small restaurants next to it, which can be solved at about 100 yuan, as well as pizza shops.
Fangte is in Hongdao, far from downtown Qingdao, and it is specially used for tourism, so it is less likely to eat affordable. It would be nice to bring something for a picnic.