This brings up a whole ball of wax...

I have Mountain Hardwear Epic and Marmot Precip rain jackets.
They both are very lightweight and pack into its own pocket.
I have worn them in torrents and stayed completely dry.
They both are very breathable*. Now I have to say,with both of these
jackets,they are waterproof,but they also have a DWR coating on them.
DWR=Durable Water Repellent

You need to read up on DWR and how to take care of it.
1 sitting by the campfire is enough to render the DWR coating useless.
The smoke from the fire clogs the pores.
(very easy to restore with a washing)

Anyway,fleabay has good deals if you watch. I paid
about 30 bucks for each of mine,new.

Anyway,I will never go back to those old,non-breathable raincoats.

(remember,the raincoat will only keep you dry
IF you have it with you.small and packable is a good thing)