Under the assumption they want to stay with Sage 100, there are no easy answers, but these are some possibilities (to get the discussion started):
1. Wait for Sage to rewrite Work Order in framework making it compatible with Premium.
I doubt this will happen, and, if so, it's 1 - 2 years out.
2. Find a standalone production package that can be integrated.
Not a great idea, time consuming and costly.
3. Spin the division off as a separate entity, install the ProvideX version on a separate server with Work Order.
On the surface this seems kind of crazy, but it probably meets the immediate need faster and easier, except for data integrations with the main entity.
4. Install JobOps (which is compatible with Premium)
You can install the Small Business Bundle with Base, Time Tracker and 5 users for $5,000 plus $1,710 maintenance, and can add up to 5 more users. Since MRP functionality is an integrated function, this price is similar to WO+MRP with implementation cost being similar.
Of course, I would do #4, but my recommendation is to wait until after the v2016 release. Sage will then have time to decide what they are going to do about their promise to upgrade Work Order and MRP to framework. They actually said that at Summit, but it's unclear as to what that really meant - like telling us about all the cool UI changes for Sage 100 and then making it a new product with new requirements. Some call that semantics - perhaps related to Rich Spring coming from Symantec.