Sorry I did misquote the price. The point is still valid..5 Ki points then.
as to upcasting, per the PHB, pg80:
Once you reach 5th level in this class, you can spend additional ki points to increase the level of an elemental discipline spell that you cast, provided that the spell has an enhanced effect at a higher level, as burning hands does. The spell's level increases by 1 for each additional ki point you spend. For example, ifyou are a 5th-level monk and use Sweeping Cinder Strike to cast burning hands, you can spend 3 ki points to cast it as a 2nd-level spell (the discipline's base cost of 2 ki points plus 1). The maximum number of ki points you can spend to cast a spell in this way (including its base ki point cost and any additional ki points you spend to increase its level) is determined by your monk level, as shown in the Spells and Ki Points table.