I will help sum it up. Quality wise I haven't handled a poor quality SKS. Some say the Chinese are worse quality, some say the Russians are worse quality, some say the Yugoslavians are worse quality. Realistically they are all about the same.
Big things to note are the following (someone please correct me if I have any details wrong).
For Soviet SKSs. There were two main manufacturers Tula, and Izhevsk. Tula produced many more from roughly 1949 until 1956, and Izhevsk made them from 1953 to 1954 (Izhevsk ones tend to command a premium). All Russian SKSs made in 1952 and later have chrome lined bores. Early 1950 and all 1949 SKSs should have spring loaded firing pins (not critical requirement or they wouldn't have removed it from production). 1949 Soviet SKSs command a premium, they have features such as a 90 degree gas block, cruciform bayonet (similar to the Chinese ones but not quite), and crude writing on the dust cover, overall those are collector SKSs though (run you at least 400$). Most Soviet production were made with hardwood stocks but some later ones were made with laminate stocks, you will also find some refurbished with laminate stocks (dealers tend to charge a premium for them). Be careful the quality of the Refurb, some have poor quality work done (most in the stores now seem to be like this, BBQ style paint on the receiver to touch up the bluing etc.). Overall follow the normal things you look for when buying a used rifle any you should be fine (i.e. bore condition, stock condition etc.). Value wise unless some rare examples will be around the 180-200$ mark.
Chinese SKSs are the other most common type to run into in Canada. As far as I am aware they all have chrome lined bores. Quality wise they tend to be in nicer shape than the Russian ones (just because most are brand new manufacture then put into the grease). Some have blade bayonets and are called Sino-Soviet SKSs as they were built with Soviet supervision with former Soviet tooling. The factory 26 SKSs are also nice as you can find out the date of manufacture based on the serial number. The best shooting SKS I have ever used was a Chinese one, but it was also literally in new condition as well. Prices seem to have fluctuated a fair bit recently resulting in these selling for 300+$ but if you wait I imagine someone will import more into Canada in the future for less.
Yugoslavian SKSs. Some were imported about 6+years ago. There are two main variants, the M59 and the M59/66. The M59 is just like a regular SKS except it has a non-chrome lined bore. The M59/66 has a rifle grenade launcher built into it but is otherwise a regular SKS with a non-chrome lined bore. Yugoslavian SKSs are not exactly common to find, and the M59/66 is very desired running at 600+$ usually.
There are other manufacturers and countries but these are just the main ones you will likely find in Canada. If I were you I would buy either a nice Russian one with a chrome lined bore or a Chinese one in VG+ condition.
