most profitable scrypt mining machine per dollar with unlimited budget and free power?
There are a few other GPUs that do a bit better according to this list:

https://litecoin.info/Mining_hardware_comparison

I think this is just based on user feedback to the Wiki.  The ones with a lot more khash/s are multi-card setups.

Really if you have free power you should mine with whatever you can afford, then add more cards after you have coins and have sold them.  There are instructions on a cheap multi-card system here:  

http://www.coinminingrigs.com/

Unfortunately many of the parts referenced are difficult to find - they sell like hot cakes!  The R9 280X is equivalent to the 7950 and is usually cheaper. 

Don't forget that there are dozens of scrypt based currencies and mining the most profitable one over LTC can net you a lot more income.  I can't post any more links here but google multipool or check www.multipool.in for a start.

Also don't forget that if you put in a nice 4 or 6 core processor you can also do CPU mining for PrimeCoin, QuarkCoin or ProtoShares.   

Good luck!