Agreed, Stylish. Some of my local races are getting a bit pricey. The main factor seems to be whether it's for mass participation and organised by a corporate outfit or smaller scale and organised by a running club or small company (we have a local husband-and-wife outfit called Purple Patch who do a lot of excellent and fairly-priced races), or for fundraising by a school or the rotary table etc.
Here in the Thames Valley I'd expect to pay £20 or so for a 10K and £30 or so for a half.
The Reading Half is up soon, at £40. I could cycle to it but on the same day is the Fleet Half, at £27. The train fare is £13 so the total is the same. I'll be doing the Fleet.
And as Millsy says, the Wokingham is cheap.
I guess it's a case of shopping around voting with your feet.