Just ask them for its chassis number. If it after GT40/P1084 it may be that price. Because its not an original car that was race or built during the GT40's racing career. The Last chassis numbered of the production was GT40P1085.
Heres a list to help. It might need amending.
1) 1964-March 1965 GT101-GT112 Ford GT's Prototypes including GTX Can Am 427 roadster, 1965 427 Le Mans, Ford GT Roadsters
2) May 1965-1971 GT40/P1000 -GT40/P1085 GT40 production run including MKII cars.
3) 1966 AMGT-1, AMGT-2 Allan Mann GT40 Lightweights
4) 1966 XGT1, XGT2, XGT-3 Allan Mann built MKII
5) 1966 J-1-J-2 J cars
1966-1967 J-3- J-8 MKIV's (note the reworked J car J-4 was used fore styling the body into the MKIV)
J-9,J-10 G7-A Can am Cars
J-11, J-12 completed in 1980's as MKIV's
6) 1967 M10001, M10002, M10003 John Wyers Gulf Mirage M1
7) 1967-1969 MKIII GT40 M3 1101- 1107
8) 1969 chassis GT40/P1086 numbered by Willment built in 1980’s
9) John Willment chassis 1087-89 I am sure these were built late eighties /nineties
10) 1971-1972 GT40/P1108-GT40/P1114 seven left over M3 chassised cars
11) 1981 1090-1120 Safir MKV's continuation cars
12) 1121 -1145??? Tenant chassis???
Regards Allan