2001 Grand Prix GTP transmission rebuild or ?

A week ago I started noticing odd behavior while cruising on the highway at speed or accelerating under light load.  On
the highway, the RPMs would fluctuate by a couple hundred or so.  Almost like it if the clutch in the trans was engaging
and disengaging very quickly.  At this point, I was not sure I had a trans problem since the car would accelerate without
issue from a dead stop or under heavy acceleration.

A few days later on my way to work, I barely got 1 block away from my house and I could feel the trans slipping.  I also
heard a subtle while form the engine area.  Almost like a power steering pump that was going empty.  I quickly turned
around and barely made it home.  By the time I pulled up, I could no longer move the car in any gear.

I checked the dip stick on the trans and it is a grayish red as opposed to a bright red color.  I let the car sit for a day and
the next day I started it.  There is a very loud whine coming from the car while idling.  The trans does appear to go into
gear now but I did not try to drive it.

I spoke to a shop that specializes in rebuilding the transmissions in my car (4T65E-HD) and they believe that that torque
converter clutch (something like that) had worn out or disintegrated and the material is spread through the transmission
which explains the fluid color and the loud whine.  The whine is supposedly caused from the pump struggling to move
fluid through the filter since it is clogged with debris. This shop is not local to me so they are not even an option.

What do I do at this point?  I assume I need a rebuild.  How do I ensure that the rebuild is done right?  I called around and
got various prices for a rebuild and they vary by a big margin.  How do I know if one rebuild from one shop is similar to
another or if one if going to repair or replace all worn items?