50MB per song :O! That sounds like your import settings are set to AIFF, Apple Lossless, or a majorly high bitrate. Read on for conversion to smaller file sizes 🙂
Bear in mind that the song limit advertised is based on 4 minute per song, 1MB per minute, encoded as 128 kbps in AAC format.
Check the encoding and file type of your songs. To do this, right click one the sorting columns in iTunes tick bit rate and kind, then click this new column to sort the songs by bit rate. Any songs that are encoded at higher than 128 kbps, or songs in AIFF etc. will be causing excess space to be used for storage. To change the bit rate and type of these songs you can convert them to AAC format (sound quality will be lost). Or you can reimport them from CD/Computer once you have changed the import settings as detailled below, but that could be time consuming.
To convert go to the edit menu, select preferences, click the advanced tab, and select importing.For best song capacity on the iPod, make sure that the encoder is set to "Import using AAC encoder", and "High quality 128 kbps". Hit OK. Then collect together all the high encoded songs and select them all (click the top one and hold shift, then click the bottom one). Right click the highlighted area and go to "Convert selection to AAC". This could take a while if there are many songs.
If your songs are all changed into 128kbps and are mostly all around 4 mins long, then you should get very close to the song limit 🙂
P.S. If you prefer, you can also convert to MP3 format at 128kbps, since AAC encoded at this bit rate and MP3 encoded will be just about exactly the same in terms of size. It's up to you which you prefer 🙂.