you have 1k and welding skills so what you can build at that price is up to you for the most part. myself I like 2 strokes and if I had a welder and the skills Id build a bike with this https://www.treatland.tv/franco-mori...ete-engine.htm
but it is a motor that should be very dependable and have more power then most people would ever need on a bicycle. but even though I like 2 strokes for my own reasons if I was not someone that likes to tinker with motors Id start with a 4 stroke but even that leaves you with many many options from motor to type of clutch.
all that said best advice I can give is build what you will be happy with.