Generally you won't find many fans of "minisystems" in a forum for dedicated source components because most minisystems are very poor sounding and therefore arn't considered 'hi-fi'.
If you want to get the best sound for 150USD you are really limited to 2nd hand components from thrift stores and yard sales or else ebay. Look out for 70's Recievers from Pioneer, Marantz or any of the big Japanese manufacturers or better still integrated amplifiers from by NAD, Rotel, Marantz or Pioneer.
http://cgi.ebay.com/NAD-3020-Stereo-...QQcmdZViewItem
For speakers look for compact American designs from Acoustic Research or JBL in similar places. Finding smaller ones will be more difficult.
http://cgi.ebay.com/Vintage-1980s-JB...QQcmdZViewItem
Older CD players seem to have become very collectible recently as people have realised that sound quality hasn't really moved on so much and machines of a certain vintage were generally build to last. You can still find bargains mainly in the 90's machines which arn't so collectible. Again look for Marantz, Nad, Rotel..
http://cgi.ebay.com/MARANTZ-CD-70-Si...QQcmdZViewItem
Or else a modern DVD player like the Pioneer DV575 is also respected for it's audio quality and of course allows you to play all the latest hi and low resolution formats from SACD to MP3 as well as playing films.
Or again you could buy a decent quality soundcard for your computer for under 100USD from the likes of M-Audio and use this as your source. TDK make some pretty nice active NXT panel speakers which are ultra compact and sound amazingly good for the money.
Lastly if you really do want a minisystem then the some of the most respected names are Denon and Teac but I don't think they would come in much under 500USD. Look for mini-component systems as a sure sign of quality rather than one box machines or even one box masquerading as several components which is a common ploy.
Again vintage mini or micro systems from the early 80's are the best quality but even these are quite collectible now days. Look for Mitsubishi, Aiwa, Sony, Toshiba(Aurex) or (Sanyo) Fisher.
http://cgi.ebay.com/Vintage-Aiwa-V-9...QQcmdZViewItem
One mans ergonomic nightmare is another retro chic...