I'm not an experienced hand here, am only posting in the absence of other responses (still early).
Have you tried CDex (probably have?) freeware, small, simple and not intrusive.
You will need an ASPI layer. Use ForceASPI to install it. Restart. Install CDex, and you can start encoding.
click here to download Force ASPI. The version works for all Windows. Unzip the file, double click the file DUMPASPI.bat to back up your existing ASPI layer (if any). Then double click INSTASPI.bat to install the Adaptec ASPI layer version 4.6 - works well with all Windows. Restart.
Then download and install CDex from click here Current version is 1.5 beta 10, don't worry about the beta, the program is constantly under development.
After installation, can use CDex immediately, no need to restart. Don't worry about the settings (unless your current job requires it - the default settings will do).
To do batch conversion, just put all the WAV files into a folder. In CDex, on the menu click Tools (I think), select convert WAV to compressed audio file, and browse to your folder. Highlight all the files and click Convert.
I've never done MP3 encoding of the scale you are talking about, so don't know how well CDex will do. Give it a try (if you haven't), until someone else comes up with a more confident suggestion.