Tinned pulses are fairly cheap and very filling. I do a pulse mix for lunch that basically involves mixing up a variety of pulses (chick peas, borlotti beans, cannelli beans, kidney beans, lentils - whatever you want) and then splitting it into portions. If you want you can add a dressing of some kind e.g. tamari, and some fish such as tuna. I find it keeps me going a lot longer than a sandwich does.