I would not recommend modifying the sear on an SKS without prior research or knowledge, in about 30 seconds with a file you can make it discharge while releasing the bolt and it will run away until empty. Took me a couple hours to figure out and fix mine, call it a learning experience.
$99 is pretty good deal.
Look I am not advocating doing it without knowing what you are doing first. But there is tons of info you can READ and figure it out pretty quick. The operating principles of a SKS trigger are far from complicated. Also a file was never near any that I have done, you are removing tiny amounts of metal at a time, checking fit and then taking a bit more off. Many SKS rifles come with a trigger that has bad sear engagement in the first place, several I have done I have made them safer to use, not the other way around.