A 50,- 100cc BBK ?
100cc sounds like just a bit too much of an upgrade for a small 50cc engine...
I wouldn't be surprised if you ran into heat issues very soon, and crankshaft bearing issues some time thereafter...
And, at 50,- I wouldn't expect the kit to last very long either...
On the other hand, if you've got a scoot or engine to spare, and you're looking for a cheap kick..