There are a lot of great outdoor jackets that can double as trekking jackets if you have enough layers to work with. My boyfriend and I have been hiking on some of our dates and found that the easiest way to prepare for the various weather conditions was just to wear layers.
We looked at getting some trekking jackets, but they were all so expensive. I ended up buying a red jacket that just happened to be waterproof. Now I wear a sweater and t-shirt under that whenever I go outside to hike.