...

2) How much longer would it take to break triple DES versus standard DES using one of the key-breaking machines described?

Using brute force, it would take the cube of the time it takes to break single DES.

Hmm... I can't figure out what it would mean to cube time. For two-key (112 bit) triple DES, it should be 2^56 times longer to exhaustively search the keyspace, with three keys, 2^112 times longer. This assumes the keysearch engine is pipelined, so each trial encryption takes the same amount of time, despite the additional rounds. Such a machine would cost more, of course, since it would have a longer pipeline, but wouldn't otherwise be significantly different in design. Back-of-the-envelope calculation: a design like the "7-hour exhaustive keysearch" engine for 2-key triple DES would take 50 trillion years or so to exhaust the keyspace. That's for a cost on the order of $1 million (it should be buildable for less than three times the cost of the 56-bit key version). Seems secure, but as Perry says,

Whether a more sophisticated techinque is possible is unknown.

Joe