Speaking personally, I would agree with upg. WPI is expensive and from my personal training experience, a WPI/WPC blend can be just as effective without the hole in your pocket.
Personally I use the Dymatize Natural Elite (I have a new found respect for non-artificially sweetened products!), but the is one of the most cost effective and also effective protein powders out there. I would suggest avoiding buying cheaper brands, because the quality of the whey will have an impact on protein synthesis. Also, just go for a straight protein to keep the costs down.
In a pre/post workout protein, based on the research I have read, it seems that whey based protein will yield best results due to the high biological value and fast absorption rates.
I would also consider L-glutamine, creatine and dextrose (get it at Big W for $2.50 a kilo in the beer brewing section!)