I have three iHome ihm60 rechargeable portable speakers which are excellent. I snap them up on Amazon occasionally for $16-$22 each. All of mine can play via USB or 3.5mm phono. The newer ones still charge via USB but may no longer play that way.
AYL Mini Speaker System, Portable Plug in Speaker with 3.5mm Aux Audio Input, External Speaker for Laptop Computer, MP3 Player, iPhone, iPad, Cell Phone (Black)
Mini Portable Speaker, 3W Mobile Phone Speaker with 250mAh Lithium Battery Line-in Speaker with Clear Bass 3.5mm AUX Audio Interface, Plug and Play for iPhone, iPad, iPod, Tablet, Computer