Here is a list of the parts from newegg:
corsair value select 2x512mb
$90 (i don't know which memory bandwidth you got but i wen with 667...just a guess)
sapphire x1950pro 256mb
$185 (i couldn't find the 512mb versioin...even the sapphire site listed it as only 256mb but if it is 512mb then an extra $30 sounds right)
I don't know what case you got (silver/blue metal case doesn't help out alot
), but if it is a mid tower then i would say an extra $50 unless you got a nice mid-tower along the lines of a TT tsunami ($115ish).
Also take into consideration that it is used so there will be some deprecation. If you have other stuff like a power supply (didn't include it since you didn't tell us what it was), os (windows xp home oem is $90 on new egg), etc, then add it accordily with some deprecation.
Hope that helps