You can hide fields based off plan selection from the Workflows tab of your plans. You can add dividers to your registration using Delimiter fields of CSS borders. You can have as many child plans as you like for your parent plans, but they only got 1 level deep (can't have children of children). This and more is described in detail within your CBSubs documentation. As far as further styling is concerned you'll need to use CSS to restyle the registration to fit your needs; can't suggest anything however as you were not specific to what you're wanting styled.

I want to have the same styling as the Joomlapolis 'professional' registrations : www.joomlapolis.com/cb-registration/registers

We're using the "rounded" template included with your CBSubs package. Simply install then within CBSubs > Settings > Display > Template select the rounded template.

Where I can set the parent plan price based upon selections in a drop down.

You can't currently, this is a custom integration we've developed specifically for Joomlapolis. It's capabilities have not yet made it into CBSubs.

Well, that's disappointing. Is there some way I can create a custom registration form that mimics yours?

No, not that I am aware.

I'm an advanced developer with the ability to sift through and create custom jQuery, PHP, etc. If there is some sort of 'changeprice' function or process that you are using on Joomlapolis, I'd be able to reverse engineer it for my purposes.

None of what we're using exists in CBSubs yet. We're planning to implement this cleanly into CBSubs core when time permits. CBSubs is also encoded so no reverse engineering is possible. You could try using jQuery to move elements around, but it'd be purely visual and no PHP to protect it.