not sure what the gas and food talies work out to, but otherwise, I proably spend in the low hundreds. This year my big purchase was $200 on snowshoes, then $30 or so each on rain pants and a hydration bladder. Other than that it was just some under $15 items: Glove liners, batteries, leki pole locks, stuff like that.
I have found that hiking is expensive in the "initial investment" department, but its not like a lot of things where you have to keep spending and spending. I admittedly have a few thousand dollars in gear, but when the shelf life of packs, tents, sleeping bags (had mine over half my life) are in the decade plus range, and boots are close to that(actually my dayhikers are about 12 and going strong, backpackers need replacing at 7), its not so bad. If I spend under $300 on gear a year its not too bad. As much as it adds up over time, consider the alternatives:
Skiing (my other beloved hobby), where you've got lift tickets which can reach hundreds a year(my threedom was over 300), golfing - which I don't want to think about, and even my gym membership is 300+ a year; hiking starts to look like it is in fact an inexpensive hobby afterall!