Check out the Marmot Super Mica.  It is a bit pricey although if you hunt around you can find it marked down considerably.  Still, given that it is truly waterproof, it is far cheaper than gortex or e-vent jackets. No waterproof jacket is going to breathe like a cotton shirt but the Super Mica has pit zips and is well vented.  i have worn it inextended downpours and stayed dry.  It is extremely light weight.  Really the perfect rain jacket for paddling, highly recommended.