With the gutter lance you clean inside the trough not just the underside as you would with WFP.
Bought my gear awhile ago now (couple years?), so can't really remember, but think it was about £500
With the gutter lance i have also washed down the side of a house for a painter.
A standard 3 bed house i would charge from £70 - £90 depending on how bad it was.
Last 3 bed i did took me about 45 mins from start to finish.