Shoes: £0 (barefoot) to about £100 a time of which I have about 10000000 pairs collecting dust from when I was a heel planter and since I've bought 5 & returned 1 pair (that did not live up to things) since I switched for forefoot. 2 pairs of the forefoot shoes were plimsoles (one @ £6/pair and one @ £3/pair) all retired. I guess I'm now down to about £50/year from about £100/week in years gone by!
Shorts: £1/pair picked up several years ago from Primark.
Socks: Still using the pile of "triathlon socks" I got for mountain biking about 10 years ago so hard to estimate the real cost. I guess eventually similar to everyone else but I will be looking out for them discounted in plenty of time.
Tops: Any old t-shirt does the trick for me unless it's likely to be hot or wet. Then I will dig out another old hi-tech top from when I was mountain biking.
Gadgets: £0 - I don't care too much about how far/fast etc. so I don't use these things now. I don't need music to run, I like looking around. I do have one from when I was biking but it refused to talk to the PC anymore after the PC cheated on it after plugging the car GPS in to update that, (also by Garmin - you'd think the duffers would allow their own products to be happy working together on the same PC but no!).
Car etc.: £0 - I just run to places I can reach from where I happen to be.
You see everyone, it is the biking that's expensive as most of the kit will be for running when you get hooked on it.
Average cost for running now - about £1/week. No, something like double that because I still get RW.
As you can tell, I mostly look like an old tramp when running but I just don't care!