Bestow + Thalia = ?

[Norm4eva]

I googled around a bit and came across an answer, yes. However, it doesn't seem to jibe with my understanding of how costs are determined in relation to the way Bestow appears to work.

If Thalia, Guardian of Thraben is in play and I attempt to cast Boon Satyr for its Bestow cost, my current thinking is that it doesn't appear to actually become an Aura and lose the Creature type until 601.2g. Once the Bestow cost is paid, it becomes an Aura and per its rules text you're now given the choice of a legal target and so on.

If Bestow actually changes the creature to an Aura as a result of Casting Spells -- 601.2b, then it would affect the cost. If I'm correct in my understanding, though, it doesn't actually happen until 601.2g (during payment), by which point it's too late for modifications.

So, at which point does it actually change types?

[bactgudz]

The player announces his/her choice to pay the alternate cost in 601.2b:
"...If the spell has alternative or additional costs that will be paid as it’s being cast such as buyback or kicker costs (see rules 117.8 and 117.9), the player announces his or her intentions to pay any or all of those costs (see rule 601.2e)...

At all points after this, the conditional of bestow's static ability in 702.1a has been satisfied:
"...If you chose to pay this spell’s bestow cost, it becomes an Aura enchantment and gains enchant creature..."
You chose to pay in 601.2b even though you haven't paid yet.

Then when costs are calc'd in 601.2e it is already a non-creature spell.

tldr; You choose to bestow in 601.2b which makes it a non-creature spell from then on.  The total cost is determined after that in 601.2e