The SKS is cheap because they are military surplus from the 40's and 50's, no way to produce anything that cheap these days.
x39 rifles rarely function reliably when converted to 223 anyway so it would be more trouble than it's worth.
If you like the SKS enjoy it the way it is, if you want something in 223 pull out your wallet and buy one, it will be a lot easier and faster than waiting for some pipe dream $300 NR 223 semi.
A Mini-14 is $1300
a VZ-58 is $1300
a Type-81 is $1000 for now, and the only way for that price to go is up
a WK180, same story as the T81, i wouldn't be surprised if the price went up to 1500-2000 in a few years.
a Type-97 is more reasonable at $800, $1000 for gen-2, but yeah, it's not exactly a proven design.
I'm thinking about something half those prices, at least. What we need is a .223 STANAG rifle that costs under $500.
and AFAIK, Norinco does still make the SKS, you can get brand new commercial versions sometimes here for dirt cheap, they're not all military surplus. I wasn't thinking about surplus army stocks. The tooling used to make them is vintage, however.
We need a semi auto non restricted for under $500? I'm not saying it wouldn't be nice if there was a cheaper option but good luck with that. The WK-180 is the cheapest a rifle can be made in North America these days and by the time you let the government, importers and retailers take their cut from something coming out of China you get to the price of a T-81, you will never see a new production non restricted semi auto for under $1000 again, If you can't afford the current options I suggest you get a better job rather than wish for a $500 semi, you'll have a lot better chance getting a better job and it will benefit you in the rest of your life as well.
How much did an AR-180B go for on retail, like $600? Try and buy one today, at least 3 grand. VZ58's were $5-600 a decade ago, price has more than doubled. I don't know why this happens in Canada, but it does. If the WK starts to drop in price it would be great, but i've never seen a semi-auto red/black gun get cheaper over time in this country.
The only flaw in your price jumping theory is that the AR-180 is a decent rifle made by an American company not a piece of crap made in China rifle. The AR180 was also $600 US 15-20 years ago not yesterday, have you ever heard of inflation? Even if you could still get one for $600 US how much is that once it is converted to Canadian and you pay someone to import it? Yup, getting close to $1000.
I used to own a T-81 and I've handled and shot a few T-97's, they work and are a decent truck gun but they are not built anywhere near as nicely as something made in the US and I doubt that anyone anywhere is ever going to spend $2000 for a T-81 or a WK-180 unless it's black market after the government prohibits all civilian ownership of semi automatic rifles.
The WK180 is never going to be a collectors rifle, it's a cheap entry level rifle and I doubt they will stop making them unless sales drop off to nothing which means the price will probably go down not up.
You are correct though, the US built AR180-B2 rifles have increased in value a little, I bought mine new in 2007 for $1400 CAD (one of the last ones imported) and from what I've seen on the EE I wouldn't sell it for less than $1800, mine is also all original and in mint condition, the ones that have been modified to try to make them more like an AR I wouldn't pay more than $1200 for.