More Cost?
At the moment I run a DR400-180 & a PA28-180 and can't slide a cigarette paper between the two of them on operating cost, so I can't think why the TB9 should cost any more than a DR400.
The TB9 may well cost less to buy but I would take a very good look at the group finances before getting involved as the low cost may well hide some big bills just over the horizon.