Quite frankly, I use the aWATTar-Binding for that. The basic aWATTar-API is open without registration and the aWATTar-Binding already spits out two things: hourly prices in separate channels and an extra Thing, which can be configured to already calculate the “cheap hours”. So I use that for starting loading the EV and other high consumption devices.
There’s a discussion going on to streamline the efforts for dynamic pricing:
But for the time being, I just use the ready-made channel-configuration with aWATTar-things. 
You can add the local surplus to the aWATTar-bridge (base price) and you’ll get the same exact pricing as you do with Tibber.