I've made a spreadsheet comparing credits to $ amount.
https://docs.google.com/spreadsheets...it?usp=sharing
It's incomplete because some prices aren't published. There are a lot of obsolete parts (which is why I'm guessing a lot of them get donated).
I was hesitant to share this because I don't want teams to claim stuff on First Choice just because it's more bang for the buck(/credit). Get what you're actually going to need, not chase the better deal.
Please feel free to edit and change prices if you find a better price somewhere else for the same (or equivalent) part.