> I have by shipping options set as a table, but is there an option to show "if over 25 then we will calculate?"

You'll need to write custom code to handle this. Steps:

a) Create a new variable in the configuration table called SHIPPING_TBD_THRESHOLD (or something like that), and set the value to 25.
b) Create a new shipping module called "TBD" or something like that which tells people they will be separately invoiced for shipping. Only enable this when > SHIPPING_TBD_THRESHOLD items are in the cart.
c) Disable the Table shipping module when > SHIPPING_TBD_THRESHOLD items are in the cart.
d) Add language to your checkout shipping page to describe this.