Iceman I go through this exercise every two years when renewing a fixed term contract.
As you say pricing is not transparent, rather they first want to know what you pay now then they claim 'their' price saves X $100s per year. It's all smoke and mirrors BS.
You've gotta ring these bxxstards up and demand their BEST Kw/hr rate and daily charge. That's the stuff that you do the calcs on. Forget sign up bonus unless you get two close offers cause it might help over say 2 years. Discounting and negotiable line charge is still around despite minister Wood-head has tried to cancel them. I usually threaten to leave straight away to set the scene. Churn costs them money. Buying back doesn't work here as they want to sell stuff not buy it.