The following is a factor price breakdown for the combination that comprises more than 80% of my lunches (n=28):
The surprising factor is clearly the cost of tofu. That said, I do use about 62.5g worth per sandwich. It still seems unfair that the least tasty part of the sandwich should cost the most. If I do end up going to London this weekend – as now seems highly likely – I can pick up some much lower cost tofu in the small Chinatown there.