Paul,
Is it essential that you measure absolute levels all the time? I just wondered if there were some way you could fit a number of cheaper level switches say 1 every 100L and gate these into an ODI.
I did a project many years ago for a health care company which had multiple tanks of different chemicals and volumes and this actually worked out quite well as we realised that effectively having 'set points' was enough.
I just know some of the level sensors are very well priced such as Farnell 167-3638.
Regards,
Peter