Keep in mind that forced labor is not even remotely cost effective.
I used to run labor crews in National Parks and BLM lands, including the occasional con crew.
A horde of motivated volunteers, or college-age labor crews from
SCA or
ACE can do an amazing amount of work, with fewer limitations on what sort of work they can do than the average convict crew can.
Convict crews require armed guards and need to be able to return to the jail/prison each day. If you want to work them further afield, you need to fork out for 24/7 law enforcement details to guard them, you need to put them up somewhere, find a way to feed them. It adds up.
The SCA/ACE crews need none of that. Little direct supervision, and they'll just camp wherever you tell them to and make their own meals. And those crews are very self-motivated, they'll work very, very hard so long as they understand what it is they are supposed to be doing, and why (they "why" part is very important to the self-motivation thing).