First my stalk had 975 grammes of sprouts on it which works out at £1.29 per kilo. Sainsbury's has sprouts for £2 per kilo this week so I was still in the lead. However, assuming that a Sainsbury stalk yields the same as mine did, I also noted that it is cheaper to buy loose sprouts than it is to buy a sprout "tree", as Sainsbury calls it.
I weighed my sprouts after I had trimmed them and found that I have 780 grammes of trimmed vegetables. That means that the ready-to-cook price is just over £2 per kilo. Some of these I have frozen, some I will eat over the next few days.
As a matter of interest I checked the price of frozen sprouts at Sainsbury. £1.30 per kilo. If cost is one's only criterion, frozen sprouts are the way to go! They win over both sprout trees and loose sprouts.
PS I have kept the top to use as spring greens as well - I think of that as free food!