I have been quoted this for 2 x 2 wood for building a partition wall....

47 X 50 MM WHITEWOOD OFF SAW TREATED 48.00 £77.02 100 M £36.97
I think the above means 48M charged at £77 per 100M rate =£36.97

Question ..does it have to be treated? or should I be able to use
something cheaper?

The wall will be this size...
Wall width (9ft 8inches 2 x lengths) Floor ceiling height (9ft 9
inches x 8 lengths)