Hello and welcome,
Here I have a how to make a Swing bike ( Mini ) in 10 steps.
Mind you, you can make a 20" OR A 24" bike the same way.
Bench and hand Grinder
Hack saw or another way of cutting
Varety of tools to take apart and assemble the bike/s
Mig, Tig, or cutting Tourch with braze rods
Drill press / drill and drill bits
Total cost for me will be in the welding, plus any new parts I aquired.
Skill level; I would put at an 8 out of 10 and about 48 hrs + .
Click on any image for a larger view.