To be honest I think that the price of Substance Painter is worth it. It's only 15 EUR a month if you sign on for a year, and you can get a perpetual licence on Steam for 127 EUR. You can also try it out for 30 days for free which seems very fair. In that time you can texture a ton of assets if you have prepared them correctly (UV and Material ID maps are already done for example), plus you can find out how it runs on your hardware.
If you really don't want to pay then Quixel Mixer seems to have a similar workflow to Substance Painter (so changing over later shouldn't be too much of a problem), but I reckon if you are serious about content creation or have a lot of assets that need PBR textures then the limitations of Mixer might well get a bit annoying after a while.
Paul