At a minimum, in order to replace the flex plate you will need to drop the transmission.
If you have gone to all the trouble of dropping the transmission it would be a very good idea to replace the torque convertor at the same time. Many times when a flex plate breaks the unbalanced nature of what is left can cause the TC to fail.
Between parts and labor it is going to cost the better part of $1K to replace the flex plate. It will cost the same amount to take the transmission down again to replace the toasted TC. And it will cost you the same amount again when you end up replacing the transmission because the failed TC sent chunks through the transmission.
I think $2K is a bit on the high side unless the interior is completely converted to something that you like.
Worst case is you will need to pony up around $6K to replace the transmission, torque convertor, flex plate, and flush the transmission cooling system.