I don't get it £840k a year for something you could do over LTE
you can get a cheap mobile from amazon for under £20 & sim cards for under £5 a month with ~ 1GB of data usage.
why not coble up some solution that uses cheap lte components and form your own MVNE to support it?
i get that the iot things are to be low power etc etc, but LTE is low power too & if these things are on shipping crates and effectively beacon every so often & this system picks up that beacon, triangulates the position and stores it on a DB, for 2000 to get ~91+% of the nation i'm sure a phone mast would pick up the signal too as there are certainly more than 2000 of them.