Nice Job.
I would do it £300, have 2 man team on it one day. Easy after first clean, you,d be able to tie extra work.
Around 6 Hours total + average 650 to 700 litres would be enough after first clean.
We do mainly commercial & buildings this size daily, & theres always somebody cheaper, we gain 1 in 3 that we tender for, one company i know would do it at £150 to £175 max by us, but leave most & mess the job up.
This would be a good portfolio building for future expansion.
Gary