I've never totaled it up, because my wife regularly asks that question.  If I had an answer, I'd have to tell her, 'cause I suck at lying.    Most of the components in my panel (SSR's and the like) were bought off eBay with CONSIDERABLE savings.  Most of the oddball stuff was bought at a local surplus store, and the rest at Home Depot.  If I had to pay retail for EVERYTHING, it'd probably be upwards of $10,000.  But I didn't, so it's OK.

2008 Answer:  Now that the panel has been rebuilt, we have moved from SSR's, towards a commercially available product.  Believe it or not, the cost is about the same.

2011 Answer:  Now that the LED conversion is in full swing, I think it would be reasonable to add 50% to the original estimate...  Don't tell Cindy.  ;-)