Hi Marcel,
I hope you are referring to the project header fields, if yes, you can give access to your project to a supplier/vendor contact if you wish to but it cannot be limited to a particular field.
On the other hand, if you are referring to a term in your event content say for example "inventory_cost" for an item, you can control the visibility of this term whether the vendor(s) can see it or not at the time of bidding or event preview period.
Regards
Vilas