shop shop shop then shop some more
you can find good quality waterproof pants - just keep looking.
I have expensive gortex pants from EMS that I got as a gift for hiking in the rain but they work great cycling too.
last year I got a great cycling specific rain jacket at REI for $50 (that was 50% off!) so keep shopping! ;-)
+1 for the clear shower cap on the helmet
for feet I use rubber overboots I found for $35.