I felt the same way as you do when I received the invite. I broke down and did the full prep and was hired.. If you want the job and it doesn't break the bank I'd say go for it. It definitely doesn't hurt your chances and you certainly won't be left with a "what if" sensation should it not work out. I am by no means affiliated with Emerald Coast but they have an audio prep for $95 that I think is worth the listen if you don't want to go all in.

I'm also curious about this and how many prospective hires they proposed for the following year.