for file in *.flac; do $(flac -cd "$file" | lame -q 0 -b 320 - "${file%.flac}.mp3"); done
You need lame installed on your linux box for the above to work. You can change the bitrate by changing the value of the "-b 320" to be what you want, maybe 192 is fine for you (or maybe you have a MP3 player that only supports certain bitrates). I like using "-q 0" as opposed to "-h" (which is really "-q 2") for the noise sharpening and psycho acoustic quality setting. It takes longer, but it is higher quality.