Sean,

just on the cost of the interior. Here are my figures incurred changing our car to black interior:
original black Dash $150
Door trims - not sure as I got them with the car
glovebox $50
Pillar trims in original black $4.50
Sun visors spray painted black $35 + the vinyl spray paint
NOS Handbrake grip $17
Centre arm rest retrimming $41.50
new Handbrake plastic cover $36.76
new Kick Panels $41
Centre console $60 + black spray paint
new Door arm rests $140
new Carpet $120
new Pinchweld $67.50
Seats retrimmed $770

Total $1533 + door trims

These are my actual costs (yeah pretty anal like that, keep all details logged) and it does not even include the funds recouped selling some of the existing interior bits I had.

Now think that I could sell all this stuff to replace with Buckskin some of which is still in the shed and I reckon I would come out even or even in front as black stuff always sells for more on ebay than any other colour.

Re-trimming seats again would be the same cost but the rest could all be obtained in pretty good condition 2nd hand on EBay or at swap meets. Remember that 63V is a very common colour for kingswoods etc. I even wrecked a car a while ago that had all this stuff in it in good nick. It is easy to find.

Now repainting. Well not sure how you can on sell the old paint and replace it with new any cheaper than the cost of a respray.

Verdict for mine:
Interior is the simplest and least costly thing to change back to original on the whole car.