Finding an application to convert from MBOX to PST can be really hard especially since all programs cost money. There are all kind of apps developed to aid you in conversion, but no one says that you will need the full version, and sometimes the full version of the software costs around $300-400, which is rather expensive and pointless.
After some extensive searching, I've found the following application: https://mboxfiletopst.codeplex.com/