The tanks are copper and can pushed out by hand with a little effort. I don't know about the US but here a new core is about $150 with a warranty. Also,most radiator shops here have an line source for cores and only need to know the cars details to get a core from stock. As i understand it,any car back to the 1920's can be sourced from NatRad.
http://www.natrad.com.au/
I do my own and have done for years.