Commodities to quickly level up and unlock engineers

Greetings commanders!

Since the data quarrel between Hudson and Winters has comfortably assured my credit reserves, I have started the road to unlock all engineers.

To level up and discover subsequent engineers, you need to rank up with them either by crafting modules (costly in materials, and there are modules I have no use of), or depending on the engineer, millions of exploration data (quite easy), bounty vouchers (quite easy as well)…or commodities.

These are colonies, so it seems to me that they do not require high cost commodities such as gold or low temperature diamonds. And to be honest, I do not see myself hauling hundred of cargos holds of low paying grain, that would only substitute plague to dysenteria.

So, do you know a commodity required by colonies that could level up the engineer in a more efficient manner compared to spending materials?
Or should I give my hopes up?

Thank you for your answers! o7