If its in as nice condition as you say it is, I'd say $800 while being high dollar is actually a fair price these days. US rifles have skyrocketed in price over the years and they're not even rare. In fact M1s are plentiful at gun shows and usually every shop has at least 1.
As far as being sought after, the rarer modles like Underwood, Rockolla, Winchester, etc. are what collectors seek out. Heres some manufacturers:
Rock-Ola Music Corporation (ROCK-OLA)
Standard Products (STANDARD PRODUCTS)
International Business Machines (IBM)
Quality Hardware (QUALITY HARDWARE)
National Postal Meter (NATIONAL POSTER METER)
Saginaw (SAGINAW DIVISION,GENERAL MOTORS)S.G.
Saginaw (Grand Rapids) S'G'
Underwood-Elliot-Fisher (UNDERWOOD)
Winchester (WINCHESTER)
Inland (INLAND DIVISION, GENERAL MOTORS)
Heres a site with info on production numbers.
http://home.att.net/~ra-carbines/history.html