It's not spec'd to run all day - not sure what gave you that idea:
"3000psi @ 13gpm (200 bar / 60 lpm). It is ideally suited for use in city centres where strict emission requirements apply and in areas that are completely or partially enclosed.
* * *
With fully charged batteries, the unit can handle up to 6 unblocking operations or run continuously for 60 minutes on full power."
Rioned has announced the production roll-out of the world’s first high-performance electric van-pack jetter.
So, you know their continuous flow and pressure spec, which sets your motor size. You also know it runs for 60 minutes on full power on a 30kWh pack which verifies your motor size if you back out pump and motor efficiency.
Their price includes their margins, so of course you can build one yourself for less, especially since there's not much scale for these. Most businesses make more on their time than paying for something that has a warranty and service, and recognize a bodge with downtime a few times a year would have paid the cost difference.
edit: they have two strings of 24v 200Ah batteries that it appears they select, so your statement of 3x is not quite correct. They have 6x as 2x 3s.