blocking agent for phosphoproteins - options for westerns used to detect phos (Aug/25/2003 )

I am looking for an inexpensive blocking agent for western blotting used to detect phosphorylated proteins (specifically, MAPK--Erk1 and Erk2). Can I use the cheapest form of BSA or is there a substitute for BSA?[SIZE=1]

As I saw on the protocol from my phosphotyrosine antibody sheet, It only says don't use milk
as a blocking agent because it has many phosphotyrosines and will adsorb the antibody.
I would say BSA works fine.