OP, you say "Change the spinning drive into an mSATA", but that's not literally possible. Does your laptop have both an mSATA slot, and a normal 2.5" laptop HDD bay?
If so, then you might just want to replace the spinning HDD with a normal 2.5" SSD. (Make sure that if you need a 7mm height drive you get one like that.)
Sorry for the miscommunication. My laptop has both mSATA port and a SATA port. I was thinking of adding a mSATA as my main drive and the spinning mechanical for only data. By the way is $193.00 a good price for a Crucial M4 256GB mSATA?