Usually how much does it cost to change a bridge and nut?

[Blazemourne]

How much would luthiers usually charge?

[Reuben]

A new nut costs fairly little, but a totally new bridge fitted at David Gage's shop starts around $400 I think. Can also be a good bit more.

[joel kelsey]

I got a new bridge from the Bass Cellar. I think it was around 350 dollars.

[mojoluthier]

I charge between $175 and $500. The difference is the quality of the wood, and the attention to detail. Both extremes are properly quartered/dried/fit. It is possible to put hours into the detail work, and an Aubert DeLuxe calls for it in a way that a Christopher does not. Mixed the metaphor, but you know!

A nut is $50 to $100.

[Martin Sheridan]

It would help if you'd fill in more info on your public profile.
If we know where you live we might be able to suggest someone nearby.