i've been to a few gun auctions recently (including the largest in north america, Rock Island Auction).
ithaca's are really nice quality. most of the ones that go cheap have been professionally restored. original condition ones in good shape will run you much more.
the remington rand's are generally cheaper in price, and nice quality too. this is what i've seen at the auctions i've been to:
colt A1's are plentiful and easy to find. the A1's being cheaper than the original 1911 model.
union switch and signals are aren't rare either, and are reasonably priced in decent shape. excellent shape ones are higher in value.
singer 1911's will cost as much as a house.
if you're looking to spend a little over a grand on one with all original parts and has not been restored, remington rand, colt, or union switch and signal is probably your best option
for an idea of value, and a detailed description with pics, go to rock island auction's website and type in 1911 in the search. loads of good info. they have prices realized too (what the guns went for at auction)
http://rockislandauction.com/search/aid/1016