Fair Price??

Grande was actually a Luxury package that went beyond trim, it was heavier and loaded with insulation. Mach 1 from what I've seen is strictly a TRIM Package. Although most people bought Mach1's with performance upgrades, it wasn't part of the Mach1 package. As far as a fastback Grande, I've never seen one, and I always thought it was coupe only, but don't take that as fact.

I checked a couple of VIN decoders, and didn't find a code for grande in 69 so it was probubly not coded seperately from the regular car. but in 70, I found this;

Body Code Body Style
01 Hardtop
02 Sportsroof
03 Convertible
04 Grande (coupe only)
05 Mach 1 (sportsroof only)

Also keep in mind, Ford did a lot of things that "didn't exist" such as special colors. So it's possible even if it isn't a standard option, that someone could have ordered the grand luxury package on a fastback. You'd probubly have to get the build sheet to be sure.

EDIT: I just found this for 69.

63A Sportsroof, Standard 56,022
63B Sportsroof, Deluxe 5,958
63C Mach 1 72,458
65A Hardtop, Standard 118,613
65B Hardtop, Deluxe 5,210
65C Hardtop, Bench Seat 4,131
65D Hardtop, Deluxe Bench Seat 504
65E Grande 22,182
76A Convertible, Standard 11,307
76B Convertible, Deluxe 3,439 299,824

it's possible that is the grande version of the fastback.