Presuming that you require a working-propotype to file your U.S.-patent-application?
First, have a non-disclosure-agreement drafted.
BEFORE you discuss your-invention with ANYONE in more than general-terms;
have them, a notary-public, (2)witnesses, & you ALL sign your-non-disclosure-agreement.
This provides some-limited-legal-protection prior to your-patent.
Contact rapid-development or rapid-prototyping organizations and request price-quotations.
Alternatively, depending on your-invention,
you might convert/modify an existing-product into your-invention?