Mr Bergstrom, average cost of temporary characters?

Ah ok, so it's best to save around 150 donuts then basically ready for when a character comes in? I really hope Mr Bergstrom comes into the game though, he has to have the sample of 'I'm Mr Bergstrom, feel free to make fun of my name if you want. Two suggestions are Mr Nerdstrom and Mr ... Bugger ... Strom' in his voice too haha :D

I'm not sure what a gil deal is though? But from what I can gather it's best to save around 150 donuts for if a character you want comes in then right? :)