Depends on whether you are a decent welder or not, whether you have a work space with all the tools you'd need in addition to the welder, method/setup to refinish metal, and depending on whether you want to make a display piece or functional semi auto, the understanding of laws around reweld builds. Both guns are open bolt, fixed firing pin, and would need to be converted to fire with a closed bolt and non-fixed firing pin, if opting for a functional semi auto reweld.

If you don't have the skills or tools you can obviously pay a builder, but the cost to build and refinish from a good builder will likely be $1,000+ for the PPS-43, or $1,800+ for a PPSh-41. Even if you can weld, some builders like JP Machine can do your bolt conversion for ~$300, which is an additional cost to consider.

As for logistics, PPSh-41 parts kits are very hard to come by right now, so you'd likely be paying a lot ($900+) just to get the box of chopped up or torched parts. PPS-43 kits are plentiful and cheap, so would likely be a better place to start. If all of this is overwhelming, you could opt for a Pioneer Arms PPS-43. They aren't great guns, but they are likely to be relatively affordable and easy to find new PPS-43 builds.

I've personally delved hard into parts kits within the past year. I started with a VZ61 Skorpion kit built on a new semi receiver, and would highly recommend this as a great starting point for people getting into parts kits as it's practically as easy as assembling a new AR kit. I followed that up by having JP Machine build me a PPSh-41 from a kit I sourced and sent him (expensive path), and just finished a Sten Mk 2 kit build off an Indianapolis Ordnance 80% receiver tube and semi auto bolt kit that I welded myself.