API spending on a budget

My company limits us to $800 a month on Claude API spending. We have access to all of the models including older Claude models.

I am a software engineer so I 90% of the time I use Claude for coding. It feels like my spending has skyrocketed once the 5 series opus and sonnet models came out.

I typically use plan mode since I am very particular about how I want Claude to implement features or fixes. After a handful of small/medium sized features in a day I can easily hit $50-100+ but a few months ago I feel like I would hover around $30 a day.

Is there any tips? Should I still be using 5 series models?