hey Nova,

Not sure what sort of dieting ideas you've been following, but have a similar daily battle with ease versus health most lunch times.

just for clarity, the goal I am coming from (mostly) here, is weight loss, with a side of trying to set myself up some good habits going forward (even after I lose the weight).
I've been basing this strongly in the Harcombe diet my mum advised me to try, which is kinda like a part time atkins approach - basically, if you DO eat carbs, they should be at least a few hours away from fats. also a strong focus on avoiding sugar at all where possible.

Here's a couple of fairly easy go-toos that have been helping me a lot over the past year.

salad: ok, it sounds obvious, but a lot of lunchtimes I just pick up a sealed salad bowl from the tesco salad section (simple side salad I think they call it - lettuce, peppers, sweetcorn etc), and add something to give it some flavour:
- tinned mackerel in chilli oil [£2-£2.40 all in, sure you could make similar at home!]
- can of tuna (salad niciosse (sp?) )*
- tub of that sandwich filling stuff, chicken or prawn mayo etc* (not great for you but breaks up the monotony! I only look at the sugar content on these)
- king prawns* (pricey, but I frigging love prawns, and they're almost pure protien :P )

*these are things I typically dump a load of chilli flakes into as well, adjust to your own taste!

another thing that has been helping me avoid eating crap at work is soup.
tesco's health range, and heinz big soup both have some pretty good varieties. if it's a little bland, add a small helping of croutons to give it some texture

I wrote over half of this, then re-read your post and realised cost was a big part of the issue for you. Gonna post it anyway, as they are some pretty cheap options in either case, but also in the hope that even if I'm not helping you, someone will gain something from it, although it seems to me that you hold yourself to slightly higher standards of what you want to put in your body than I do!