We went down this road when we went to Ireland because it rained or at least misted everyday.
Here are the features we both opted for:
Soft outer shell, keeps the scruffy rain jacket noise to a minimum
Breathable, you’ll likely have it on all day. At least get pit zips so you can get some air.
Stretchable, makes movement easier.
Hood, no fun having rain down your neck. Get a rain sombrero too.
Packable
Almost all the quality manufacturers will have jackets with these features. North Face, Arc’Teryx, Patagonia, Outdoor Research.
Expect to pay $90 - $150.
We had a North Face outlet near us and picked up the previous year’s model for $40, but not everyone has access to an outlet.
Kept us dry the whole time.
Don’t forget about waterproof shoes. It’s takes a long time for shoes to dry and cold wet feet are no fun.