I was going to suggest Subway, but I see you mentioned that. I usually get a mix of spinach and lettuce and then tuna, but lately the cold cut combo because no no on the tuna. It is about $5 and tax without the added drink/chips, so every once in a while it is not bad. I keep packets of WF individual packs in my desk.
I was shopping last night and realized how much cheaper it would be if I just cooked up chicken on a Sunday and had it for the week. So, I bought cottage cheese, lettuce, tomatoes, frozen vegetables, frozen chicken. It really is cheaper but the problem I have always had is that I suck at prep work. Maybe cooking at the start of the week and bagging it up might help you, too. I am going to try this week.
Have a good run!!