20 metres of guttering either side works out at 40 metres, on an industrial unit its whether you go in high as its commercial or lower to help to secure the job; but if theyre trying to rent it out theyre more likely to be prepared to pay a higher premium.
I think 250 is a fair price for in and out so long as outs arent too ingrained. I hate pricing gutters without seeing them, for all we know they could be preformed concrete, smothered in moss, 8" deep and 10" from front to back needing a skip to take the crap away.