I have used a dremel 4000 one year. you can use any of them just perfer a slower speed. The one Mr_Synical was referring to, is a low speed battery powered one. As a haunter I personally wouldnt waste my money on it but not everyone is a DIY.
Since Funkins are soft you can use almost anything.
If you're just cutting then use cutters like:
The Pumpkin dremel uses a High speed cutting bit "100 High Speed Cutter "
I found the "561 MultiPurpose Cutting Bit" to be pretty good at cutting foan holes.
if you are adding some thin lines use an engraver bit.
I do recommend getting a spare one to practice and test bits to get the desired speed and control.
But