There are many ways to make quiet MP3 files louder ("Normalize"), but the easiest is by far using Audacity, since you can process multiple files at once (also known as batch processing) with the Macro tool:
To save paper, consider printing on both sides of the paper (duplex). If your printer is able to print on both sides and is installed to support CUPS, you can define default setting such as changing paper size from Letter to A4 and duplex printing to "Two-Sided: Long-edge binding" at http://localhost:631/.
QGIS is an open source program which allows you to: "edit, visualise, analyse and publish geospatial information on Windows, Mac, Linux, BSD and mobile devices. For your desktop, server, in your web browser and as developer libraries."