The question depends in the volume you think you might have and the hydration of the dough.
I would think a min of a 30 qt hobart, these are 220 typically good used about $1500 ( if lucky) to $2500
A larger is a 60 qt, hobart h 600, decent mixer, about $3500 to $4500
Strongest is the p660 60 quart it's a 3 phase, you can buy a PhaseMaster to convert single to 3 phase. They work fine. Best deal $3500 range up to $7000
If you mixing low hydration dough, the h 600 and the 30 qt will struggle, so you will need to reduce the batch size. Or the p660 which can handle tough doughs all day long....
If you are just starting maybe try a 30 qt hobart
Low hydration is in the 40's, at 45 and below with low oil <3-5% the h600 and 30 qt will get beat up pretty bad, you will have to reduce the batch size. If your dough has 50% and up then either will work great for you at full batch size. Just speaking from my experience with these mixers...