1. Select the WAV file in question.
2. In the iTunes menu bar, select File -> Create New Version.
3. If it offers only to create an AAC version, you can change this to MP3 by going into the preferences and changing the import preference to MP3.
Yes you can Right/Click or ⌃(control)+click the file to highlight it and bring up the Contextual Menu. Scroll down until you see Create either wav, ACC, MP3 and if it say MP3 click it, and you now have a copy of that song in MP3.
If it isn't MP3 follow these instructions to change it to MP3.
Choose iTunes > Preferences, click General, and click Import Settings.
In the Import Using pop-up menu, choose the format you want to convert songs to, and click OK to save the settings.
Select one or more songs in your library and choose File > Create New Version > Create [format] Version.
Once thats don't Right click and bring up the Contextual Menu, now when you scroll down, it should say MP3, click it, and you will now have a copy of that song in MP3 format.