Looking at all the battery types (as in fixture) the  wall mounts are the most costly, the rack mount and floor ones are about the same and the "truck" type the cheapest.

I  think the case for rack mounts are excessive as they are a 4U server box, which are around £80.00 to add the £5 connections, the £150 BMS and a hole in the front, a non cut back panel is not worth the £400+ price tag. That being said the wall mount is a little more in cost but you have to use better grade steel.
With steel being around £39 a sheet as well.

The bottom price "truck" battery is a ABS case with terminals, maybe a meter of some sort, but they function as a lead acid drop in. for those with LA batteries this may be "no real change" but depending on the installation location ( and withstanding the new rules) they may not be practical. We did come across  some nice metal cases. which are smaller but they did not use prismatic cells, though apparently they did in the bigger ones. they also have an Anderson connection, which was a 50 amp connection.... for a 100amp output!  not ideal, but that depends on the use case.

Cells are down in price as Im sure you know, so that bare bones of a battery is NOT expensive, but may factor the shipping which can be costly. trying to find a UK battery case is a pain and I have looked into having one made.