Is there a formula for the price of casting permanency?

[Pomkin]

For spells not on the list of allowed spells?

For instance, if I wanted to make grease permanent is there a set price, or is it something the GM would have to make up on the spot?

[Chemlak]

Essentially, it's (min caster level - 8)x2,500 gp, where min caster level is 8+spell level.

However all non- standard spells are GM's discretion only.

[Randy Lockard]

I would agree with the 2500gp as other 1st level spells are. Chemlak is also correct in the fact that only a DM can approve non-standard use of the spell (as Grease is not listed).