The surprise was that, although I've found some $20 tools with free trial (e.g. mp3-speed-accelerator), I couldn't find truly a free tool.
The magical search string "mp3 speed -shareware -buy -order -trial -usd -now" didn't help me find anything useful. Also tried various variations of mp3 resize, mp3 shorten, podcast compress, audio shorten, audio speed, looked at SourceForge and in other places.
Looks like a good oportunity for creating a popular (truly free or really cheap!) tool with minimal effort.
I can use lame to transform mp3 to wav, then apply my tool, then use lame to make mp3 again. Manupilation of wav files seems to be very simple:
1. Spec: http://www.microsoft.com/whdc/device/audio/multichaud.mspx
2. Example: http://www.codeproject.com/KB/audio-video/CWave.aspx
After all, there are sources of lame (out there in the wild...).
(The problem became actual after I joined SHMIAk school. I can hardly afford listening to 60-minute long lessons, so I need to find a way to save time without loss of information).
Upd.: A good free tool found: http://audacity.sourceforge.net/, business project cancelled! ;)