You are all correct. The key is to not think of the infinitive as a standalone part of speech, but a functioning unit of language. Look at the phrase's function, and it will show the part of speech. It will be a noun, adjective, or adverb.
Noun --> "His job was to help me." (What was his job?)
Adjective --> "There is a file to ...
It means that in answer to a formal procedure making explicit that someone (company, business) is accepting propositions for doing a particular job for them, these propositions having to do with the means intended to accomplish this job and the price that is required (if that price has not been fixed), you make such a proposition.