How many yards do you need to do the sheets? If just doing the corners and would only have to do 3 corners since you could use one of the original ones on the kings size sheet and 2 if the sheet is same length as the queen bed. Are you putting the elastic all the way around the sheet? If you are only doing the corners I would think 15 to 18 inches per corner would be plenty. So 3 yrds for $5 is not bad considering you could get 4 corners out of the package and you could not buy a fitted sheet for $5. Oh just remembered you were only using the top flat sheet, but still could do one or more sheets for $5. Good luck, take care.
Linda