Create record in Base 2 picking from data in base 1

[MDDDDDD]

I have a base with Costs and I want to set up a form where our staff can select multiple records data from one base that will then create a new record in a different base. I want these new records to only show the data selected in the form. 

This base has unique 'cost code' fields and a corresponding 'Nett Rate' field. I want them to be able to select multiple 'cost codes' that will then create a new record with all of those selected cost codes and Nett Rate fields 

I then want to set up an automation that sends that record as a CSV file to an email address

[TheTimeSavingCo]

Hmm, if I were you I'd:
1. Have a new table with a form in the 'Costs' table, allowing users to select the records you mentioned
2. Have a third party service like Zapier or some such trigger when an automation gets created in that new table, and its action would be to create a new record in the other base, with the data you want

If possible, I'd add actions in the same Zap that would convert that data into a CSV and do the emailing for me.  Highly dependent on what actions are available to you based on your budget though, so might need to be a separate Zap too