I would go for 2|2 for 5 unupped and upped
Seems like a bit of steep drop between upped and unupped cost.
More accurately, 5
seems too steep for the unupped version.
Skeletons are free for 0
both upped and unupped.
the upped are even 2|2 creatures.
Granted the ability here warrants some cost bump, but if it has a decent activation cost then it shouldn't be huge problem.
I think 3
maybe 4 tops is good for unupped.
Upped cost seems fine though.
... As an interesting idea, why not make it 2
and 1
but be a 2|0 or maybe 3|0.
The reason being that this thing can buff itself on the first turn, but doing so would require expending an alchemy spell and paying the cast cost.
Requiring expenditure of another card more than makes up for any casting cost deficit here (in fact it may be viable to make at a 2|0 and 4|0 for no cost at this rate).
So its spark like but can self perpetuate if it is comboed with at least one alchemy card plus its skill cost.