I recently ordered another package of random choice wool on eBay - the seller's choice, that is. It's ideal for blankets and I still have left-overs from the previous package I bought from her. At £10 for 16 balls plus £6 for postage that's just £1 a ball, no slogging round the charity shops to see if they sell wool (some do) and paying about £1.30 for it, though admittedly you are buying your choice of colour, if they have it. Wool shops are hard to find, in fact, I don't know where there is one! This comes to my door neatly packaged..
I reckon 5 strips make a blanket about 45" wide and I've just started strip No.3 of blanket No. 3 in the current series.