Real time Update Field B on update of Field A

The user creates a New Record. Then : 1. Picks Service Provider (User Entered) 2. Populate Rate List Picklist (System) 3. Add Service (User Entered) 4. Populate Cost from rate list (System) 5. Margin (User Entered) 6. Price (System Calculated Field Autoupdates, real time, Pre-Save) I want this real time since they have to do this multiple times on the Line Items. The rate list is different based on the service provider and there can be a different service provider per line. Rate List (Like Price List but also has a Service Provider ID or Account ID) Rate List Items (Like Price List Items) This is the ideal user experience. I think Step 2 can be done through a custom Field render but the rest not so sure.

Ivan, you can totally create effects like this using Javascript custom renderers and dependent picklists.  Below is a link to an example Zach wrote creating somthing similar using opportunity line items.

One point of caution:  Your real time calculations need to match any server side processing that is set to occur on save.  Otherwize the real time changes will be over-written on save.  This has been particularly challenging with standard objects.