There's no reason to pay for it! It has no value!
In terms of procedures, decision making, piloting, etc, I learned more in a few hundred hours of flight instructing at ATP (especially the instrument instruction) than I did at expressjet.
What did expressjet teach me? They taught me about the ERJ-145, how to start the engines, what oil pressure range the engine has to stay in, go to amazon.com you can learn about the ERJ for $50. Yeah I learned (a little, relative to other more experienced pilots

) about the technique of flying the ERJ too, when to put the flaps down, how to handle different situations ATC loves to put you in. But when you're looking at "The Knowledge It Takes To Be A Pilot", that's
tiny relative to learning the fundamentals; how to safely operate in IFR conditions, and the countless other things you'll learn and master during your initial training and as a CFI. And you already said you're going to CFI anyways, so you're going to have the opportunity to learn these things first hand. Listen to the captains complain online about their crappy FOs, what are they complaining about? FO's that don't know the fundamentals. In contrast every captain I flew with was more than happy to give their opinion or explain their actions in those weird airline-only scenarios that occasionally come up.
So what are you getting for $25,000? You're buying a little bit of practice about the technique of flying the Beech 1900D.
If I had to apply percentages to the value of all of your flight training....
Training up to CFI - 45% ($50,000)
Working as a CFI - 45% (you get paid)
Working as a FO - 10% (you get paid)
Pay $25,000 for a glimpse at that last 10%? Not worth it.
The other argument people make is 'it's worth it because I'll get to see airline training ahead of time'. People see working as an FO as some huge jump in skill or knowledge, it's not. It's a perfectly reasonable and normal next step if you've built a strong foundation. You don't need to pay $25,000 to get a glimpse at airline ground school. You dont need to pay $6000 for a pseudo CRJ course. You just need to master the basics (by being a good CFI, especially the instrument stuff), and airline ground school will be a smaller step than getting your CFI will be.