You can buy an LS1 crate engine for $6K brand new.
http://www.sdpc2000.com/catalog/120/...te-Engines.htm

The new 5.7L hemi is >$8K. http://www.mopar.com/muscle/whatshot.htm
I know Viper crate engines are available. I've seen ads in magazines. Any Chrysler dealer should be able to find out prices. It wouldn't surprise me if the price is >$20K brand new. Your best bet would be to shop around for a totaled car.

Since the SRT8 isn't in production yet, I'd say the availabilty of it is zero right now.