What you can do and what is sensible are very different. To me using pvc covered wire is stupid beyond question, but it will undoubtedly work up to a point. The best stacking factor you can manage with enamelled wire is about 60%. With thin pvc coating you would drop this to below 30%. The big factor is the temperature limit, I think you will be hard pushed to get pvc to survive 60C whereas the class H enamel coatings survive 200C.
You will need something the size of a 2kW conventional alternator to give you 100W. It will cost you far more in the extra magnets to save a small cost on copper. You will need to wind many strands in hand or use lots of parallel coils.
I can't even see the justification for using second hand magnet wire but that makes a bit more sense although it may cause more trouble than it's worth.
For most of us there is no saving in money from renewable power, it is far more costly than grid power. If you are not on grid and rely on it you had best not cut corners or you will pay dearly. If you are doing it as a hobby then ok have fun but you may be advised to spend precious money on more worthwhile hobbies.
Flux