[1985 CCX]

My $0.02 CORRECTED............

KMS/CSX are the same car in alloy and will be well north of $100k to start particularly if you are going buggy spring.

Remember std KMS is like an ERA 289 car, a hybrid using a 427 chassis.
KMS upcharges for buggy spring chassis Big$$.

SPF is a great option as its both CSX glass and SPF using buggy spring chassis.
I love ERA cars but I would pay the extra few bucks for SPF as its buggy spring and not a Hybrid chassis. More correct. Glass CSX cars are SPF cars.....

Top down:
CSX alloy expect finished price >$200k
KMS alloy expect completed at >$200K buggy Spring ($less hybrid chassis)
CSX glass ~ $140k buggy spring
SPF glass ~ $110k buggy spring
ERA glass ~ $100k glass / hybrid chassis

Of course I menatlly added things for correctness which could change $ but this should be about right in the end for decision making purposes.
The base car is mearley the start as motor, trans, wheels, tires adds $$.