I paid 700 dollars for a 13" x 42" 'roundhead' Regal lathe, built in 1943. Fully tooled, in good condition, with taper attachment and single phase motor.
When determining price or "salability" of a used machine tool, it comes down to three words: "Condition, condition, condition" and a fourth word: "tooling".
The old LeBlond Regal lathes of the late 30's-40's all had threaded spindle noses as standard equipment. If the lathe has faceplate and chucks furnished with it, this is a plus. If not, the only way to mount chucks or a faceplate on the threaded spindle nose is to machine backing plates from scratch as no off-the-shelf backing plates or faceplates are available.
Headstock gearing in these lathes is quite light. This is a weak link in 'lumphead' (predating the roundhead) as well as 'roundhead' Regal lathes. Abused lathes of these types often have damaged gearing in the headstock. Busted teeth are the mode of failure. Some used parts appear on eBay, but the only other recourse is to make new gears as replacements. Before listing this lathe for sale, it is a good idea to open the top cover on the headstock and be sure the gearing is in good condition with no damaged teeth.
Otherwise, these are good little lathes, very user friendly. I have owned my 13" Roundhead Regal since 2012, and really enjoy using it and am impressed by what it can do for a lightly built lathe.
Price of a used lathe is also a function of geographic location. Some areas of the USA are virtual "deserts" due to a scarcity of used machine tools, particularly of the size/type/price range for home/hobby machinists. Other areas are more plentiful.
A lot as to pricing and condition depend on the history of the lathe. If the lathe were purchased new by a home-shop machinist who used it with care and lightly, the lathe gets highball price. If it came out of a school where students crashed the compound into the chuck jaws and the lathe received spotty maintenance, or from an industrial location where the lathe was stuck in the back corner of a maintenance shop, the value drops dramatically.
I was happy to get my LeBlond roundhead Regal lathe for 700 bucks. It is what the seller asked, and I did not bargain with him. I said "yes" as soon as he named the price. I'd seen two other 13" Roundhead Regal lathes for sale in my area for 1200-1500 bucks apiece. One lathe had the long taper spindle nose (more desirable than the threaded spindle nose) but no taper attachment nor did it have a chip pan, and was otherwise fully tooled, including a Jacobs rubberflex collet chuck and collets.
The other lathe was also well tooled, no taper attachment, and had a chip pan. I wanted a lathe with a taper attachment and was in no rush, since I have a Southbend Heavy 10" lathe (w/0 taper attachment). When this Regal lathe came along, I jumped on it and consider it a good deal. I got:
-3 jaw chuck
-4 jaw chuck
-steady rest
-follower rest
-faceplate
-dog or 'catch' plate
-arbor with drill chuck for the tailstock
-a few toolholders for the lantern type toolpost on the lathe
-metric transposing gears for cutting metric threads, an unexpected bonus when I discovered them already mounted on the lathe
-a few extra loose change gears
-factory flood coolant system with original 'Gusher' pump
The lathe was within about 25 miles of my house, so not a major ordeal to get it home. Another reason I think I got a bargain.
If the lathe the OP is wanting to place a value on is a "Lumphead" Regal lathe, I would put a lower value on it. The Lumphead was LeBlond's first effort in the Regal line and has plain bronze headstock bearings, and some were built without the quick change gearbox (meaning loose change gears, another drop in price).