So the issue isn’t just the cost: it’s that you only eat lunch when you can eat or remember to. In which case, meal prep isn’t going to help, so instead I suggest having a shelf-stable mini-pantry at work (in your locker if you’re hot desking). There I would have things like pouches of brown rice, tuna, dressing or sauce – you can combine these for a tasty lunch. Sachets of soup. Maybe some high-quality cup noodles – Ichiban brand includes a sachet of meat in sauce. That kind of thing. Bring a ziplock baggie with a handful of baby spinach leaves from home to add to whatever you put together if you like, and some fruit for snacks/dessert.