I cannot imagine that the cost of you buying the small Novak's, then paying for competent installation would cost anywhere near what they want for it. To say nothing of the fact that your slide, with its serial number, and your frame are no longer matching.
That is, if you were just planning to order the slide unit itself from Mak.com. But, I went to Beast's site and saw what you were actually talking about. That does sound really nice! You would STILL have less money tied up in it than any .380 out there in a more powerful, reliable package with slicked innards and a better finish.