OK, just spoke to the UK part of Valence, and although it is twitchy about shipping one-offs because of all the engineering/customer support calls they want to avoid fielding ("Where do I measure the SG and put the distilled water?", etc, I imagine!), pricing is similar to the US and indeed better than list, circa £1000 for the U27-12RT which has ~1.5kWh usable.
Valence seems less twitchy about shipping one-offs of their new Epoch range due in September because it thinks that the Epoch will be easier for ordinary users to handle (fake holes for distilled water B^>) and a little bit cheaper too.
So, current pricing ~£700/kWh usable, cf £200+kWh for sealed lead-acid when I last checked.
A big premium, but at about 1/3rd the weight and 1/3rd the volume of a comparative SLA (eg Victron 12V
200Ah AGM Deep Cycle Battery 238mm x 238mm x 522mm 65.0kg) and prices falling, that's looking very interesting.
I think I know what I might want as a birthday present to myself if I'm solvent!
Rgds
Damon