Clontech YEXpress Yeast alternative protocol

[Peter Becker]

Hello yeast experts,

we want to express GST fusion proteins in yeast using the Clontech
YEXpress Expression System. In their user manual they recommend a 
protocol making use of zymolase for preparing protoplasts. The problem is 
the incredible high price for that enzyme.
Can somebody recommend an alternative protocol avoiding the zymolase step? 
Just to keep the project payable... ;-)

Thanx in advance

Peter