I am remodling my master bath and want to extend my shower into my master closet.

Code:
FROM:

      OUTSIDE  
__________________________ 
  |      |   | /    \ ||##|
G |      |:o |( tub  )||()|
A |      |___|:\____/ ||  |
R |     /    T--------T|/ |
A |      |              __|
G | mst  |__            /
E | clst |. |           \
  |      |()|         
  |      |. |_______ / \
  |      |\     .().|
HW|______|!\________|
()|WASHDRY|
  |       |
 /       /
__|_______|

TO:

      OUTSIDE  
__________________________ 
  | |        | /    \ ||##|
G | |:     o |( tub  )||()|
A | |________|:\____/ ||  |
R |     /    T--------T|/ |
A |      |              __|
G | mst  |__            /
E | clst |. |           \
  |      |()|         
  |      |. |_______ / \
  |      |\     .().|
HW|______|!\________|
()|WASHDRY|
  |       |
 /       /
__|_______|

In side the closet, I have already removed the drywall to reveal the supply plumbing:

    
    shower
     head
     || 
     ||
     ||
    {vlv}
    || ||
    || || 
  __|| ||_
 /__ | |__\
//  || || \\
||  || || ||
||  || || ||
||  H   C ||
--------------
SLAB SLAB SLAB
I can only assume the two outside pipes go back down into the slab to make the runs to the tub. I can also assume that the tub has a similar offshoot on the cold to service the commode.

Is it possible/feasible/cost effective to break up a small section of the slab to relocate the 2 pipes for the run to the shower into the closet 3-4 feet? Or is it cheaper/easier/better to just run all new lines using the exterior garage wall into the closet? My main reason for thinking it is better to just go backwards was that I was not planning on extending the shower all the way to the exterior garage wall.. so I would have to either go into the slab to cover there or bring it down from the attic.

Thoughts? Any rough estimates to perform this work if I handle all the demo myself? How deep & wide into the slab would I need to go? Building the shower onto a step-up platform is not an option (personal preference).

If I do sledge/cut/chisel/scratch out the slab, how worried do I need to be about post-tension cables? How would I even know if I have them?