You can get some good deals if you stick to the sale items. Be careful though of the other yarns. I checked a few against Joanns prices -
Patons Classic Wool
YBTB is $6.29 a ball Joanns sale $4.00 regular price $5.99.
Sugar and Cream Stripes
YBTB is $2.60 Joanns regular price $2.19