dental students perspective: if you actually mean a filling and not a crown/cap, i'd say white. The tooth coloured one is much much better for your tooth, doesnt make your tooth as weak as the silver and looks so much better. And white fillings can last for years and years- 10 years even (this can vary, but it would last the same time as a silver filling if not longer). The most likely reason it would need to be replaced if you have decay underneath the filling, but you could get that with silver too.
If you have the money- white definately.
I didn't know you could get gold filling- gold crowns you can, but not gold fillings.
My dentist charges around £35 per white filling- on top of the NHS charge, so your charge is about right.