i do this type of thing as part of my job
price wise theres a few things to consider
1. depends on what car it is
2. depends on how far you wanna go with the car
3. depends on why you wanna do it
4. depends on how you want it done
5. depends on who strips and fits everything back in the car
thats just the start
i just did a Honda S2000 2 weeks ago
moved and hid all the wiring in the engine bay and moved all the ugly modules and shit from the engine bay
moved heaps of shit around inside the car as well
its not a cheap job because of the time it takes