I actually didn't mind the red too much when the top half of the dash was black/charcoal like the grey and tan interiors.
I'm sure you could piece yourself together an entire grey interior after a few trips to Cophers. There are TONS of Foxbodies at any given Copher U-Pull-It. Craig and I saw was a 4-banger coupe with absolutely perfect grey interior about 3-4 months ago.
Based on the pricing from Cophers for various interior parts for my old 240, I'm betting you could get a complete grey interior with seats for well under $500.
Blue Oval Corral is also a good spot for interior parts.