This happened to me recently on the Great Manchester Cycle. Took the wheel to Evans and the fitted a new spoke for £14 - listed as a wheel true. Took it in at lunchtime and they had it done for 5.30pm.
I will remember that for future! In the meantime I've ordered all the bits I need including tools, for £20 so will have a go myself tomorrow night!
Looking at a few guides online it seems quite straight forward.
Rob



14000t of climbing! 