The 773 was a one year only item. It was available in two sets, one a freight set with several operating cars and the second a passenger set with 3 Madison cars with Silhouettes, also one year only. These sets were the top of the Lionel line in 1950, in the $80-90 range. The were available for separate sale as well.
In addition to the locos Dennis mentioned, Lionel did issue repros of the 773 as the Century Club and again as a Post War Celebration series in the repro of the 1964 freight set . This one used the longer die cast tender from the 700e . Both of these are nice runners m smoke well and have sounds and TMCC .
As for Post war interest and value, nice stuff C-7 or better seems to do very well in auctions and on the on line auction site, with lots of bids.
If you have a bit of Post War interest or are a fan of Hudsons, thw 1950 773 will appeal to you as an iconic piece.
You can never have too many Hudsons