You can buy an internal BDXL burner for $70, so they're not that expensive.http://www.newegg.com/Product/Product.aspx?Item=N82E16827136250One
blank 100GB BDXL disk costs $80
A 5-pack 100GB costs $255 here: http://www.digistor.com/Blu-ray-Recordable-Media/100GB-BD-R-Printable
I searched and couldn't find any 128GB blank disks. I'm sure when they're available for sale they will be even higher than the 100GB disks.
I doubt there will ever be movies released on BDXL disks.