GOT IT. THANK YOU kobra & DrByte. Couldn't have got it without your excellent help.
Not sure if this helps anyone for the regular Contact Us page, but for anyone else wanting to add extra Fields to the "Call For Price" Contact Us page, these are the steps I used:
1: includes/templates/YOURS/templates/tpl_contact_us_default.php
add lines for the new Field you want.
This is the creation of any new Field, with the variable
$....
This variable is crucial for Step 3.
2: /includes/languages/english/YOURS/contact_us.php
change the name you want displayed for the Field.
This file displays the name of the Field the way you want
it to show on the web page.
3: /includes/modules/pages/contact_us/header_php.php
Thru the entire file, add lines as needed for the variable $.... that you created in Step 1 (tpl_contact_us_default.php), and add instances as needed for the variable $. . . you created. This will send the customer-supplied information from the Field to you via e-mail. (I was unable to place this in any override folder).
Lines for insertion are approximately 17, 23, 52, 55, 68.
If you know of a way to place the header_php.php file in an override folder, please let me know; I tried several places, but without success.
Thank you again,
Jay