... something comparable at the time of the replacement... there are companies that will insure for replacement value.
It would be useful to know what exactly the OP considers the replacement cost, equalling $4,500, to be: historical retail price of new items when they were in production (or still available new in stores)?
The same question for Bob: what did you consider your replacement cost to be? And what you consider, in your case, "something comparable at the time of the replacement"?
Of course insurance companies would insure for "replacement value" (for extra premium). The real questions is if our (e.g., yours and mine) definition of replacement value is the same as theirs. My guess is it is not. They tend to skew definitions in their favor. For instance, if you bought a 46" TV for $1,700 some time ago, and it is stolen or destroyed, you will not get a check for $1,700. Instead, the replacement value would be based on the current price for 46" TVs, which would be more like $700 or $1,000.
So, the only thing comparable with a Contax 645 kit would be another Contax 645 kit on the second-hand market. Which would be around $2,900 (under assumption that the OP paid an average price).