Is there a form widget that does the following, as described below:

Select an event to register for from a Master Event drop-down list.  Based on that selection, a new drop-down list opens with a list of sub-events available for purchase in that Master Event.  I'd like the user to be able to select multiple sub-events.  Based on the sub-events selected, the total cost is calculated by the form, and the user can then pay through PayPal.  I'd also like to add the option of selecting a New Master Event, in case the user would like to register for a second or third event.  The Dynamic Drop-Downs widget seems to be the closest thing I can find.  I do understand a bit of HTML, but am not very confident in modifying code to customize an existing widget. 

The easiest way to set this up would be to have your master list of events be a regular checkbox field.  Then, you would conditionally show sets of fields based on the selections made in that checkbox field:

https://www.jotform.com/help/196-Hide-or-Show-Multiple-Fields-at-Once

You can assign your options calculation values:

https://www.jotform.com/help/301-How-to-Assign-Calculation-Value

Total those up in a calculation field:

https://www.jotform.com/help/259-How-to-perform-calculation-in-the-form

And pass that total to your PayPal field:

https://www.jotform.com/help/275-How-to-Pass-a-Calculation-to-a-Payment-Field

If you have any questions regarding any of this, let us know and we will be happy to help.

Please see the screen shots below.  The first is my form so far, and the second shows where I've assigned calculation values to the checkbox field at the bottom of the form.  When I use the Calculation Wizard to total the selected checkboxes, the Wizard only allows me to select the entire Checkbox field, rather than the individual checkboxes.  What am I doing wrong?

I have checked your form and I can see you have added one field only, do note that when you add this check box field to the calculation it will be taken as one single field even when it has more options. 

If you would like to display separated options then you will need to add one check box field per option, this way you will be able to handle these options in the calculation field as well as conditions, showing and hiding the needed options based on other fields selections. 

For example, I have modified your current field "TOURNAMENT EVENTS" and added 4 events, then added another 4 check boxes that will work as sub events of each event.

Here're my fields: 

Then the condition that you will need to use to show each sub event properly should be like this one: 

Here're all the conditions that I have in my form for all the events and sub events: 

This way you will be able to properly show each sub event based on the main event selected, here's also a guide about showing/hiding fields based on other fields selection or input: How-to-Show-or-Hide-Fields-Base-on-User-s-Answer

Once you have your conditions working then you will only need to assign the calculation values, get the total amount in the form calculation widget and then pass it to the payment field, the guides provided above by David will help you with that. 

Here's also my cloned form of yours where I have applied this change: https://form.jotform.com/63395488736978 

Then once the fields has been added in the way I explained you will be able to include each event and sub events in the calculation: 

Here's also a guide that will help you to clone my form so you can inspect what I have done there: How-to-Clone-an-Existing-Form-from-a-URL

If you have any question, please let us know. 

Thanks for this thorough response.  I really appreciate it!  I guess the logic of having a check box field with multiple selection and value assignment possibilities but only returning one value is escaping me. Does this field in the image below assign individual values for each of the checkboxes?  What can those values be used for?  Seems like the code would be easy to write that would allow for this one field to return a summed value based on the multiple selections the field allows for...  Maybe I'm missing something?  

"this one field to return a summed value based on the multiple selections the field allows for"

That's exactly what it is doing, each check box option has it's own value, so in the calculation widget the summed of all the options that were selected in the Check Box field:

Note: it is currently doubling the amount because of how you have setup the calculation  in the Form Calculation widget:

If you want to avoid doubling the amount, remove the calculation formula, example:

Let us know if you need more help.

Awesome!  I knew it was operator error on my part!  Thank you for hanging with me until I understood!

You are welcome! Feel free to contact us anytime you want to, we will be glad to assist you.