I have four PA systems - a 600 watt one for larger venues, a Motion Sound stereo amp for mid-size ones, a mono Peavey KB300 (my old workhorse) and a couple of sets of Yamaha YST-MS50 (80 watts) for the more intimate private affairs of up to 50 people, usually at the private (but very upscale homes). I find that the Yamaha (computer) speakers are more appropriate for many occasions than the Motion Sound amp. Sure, it is built more sturdily, but I could have bought 10 MS50s for the price of the Motion Sound, and IMO it certainly does not sound 10x better, if at all.

If the appearance was the determining factor for professionalism, I would say that there is NOTHING new which costs $50 AND looks professional. In fact, my advice to Phil would be to look on E-bay for a used Peavey KB300 or KB300A amp - he may get it for $150, and they provide enough volume to cut through the sound of the rest of the band. It is big and heavy, but it does look professional and is quite roadworthy. It is not stereo (only mono), but neither is any other suggestion made here, save for the Logitechs.

As for some of the posts above ripping "comuter" speakers - I do think that when someone tries to give advice about something they have not tried, that is bad advice.

It may seem counterintuitive to someone that "computer" speakers may work well for certain/many types of gigs. Nonetheless, the majority of people in this forum have also parted with the notion that arranger keyboards are less than professional instruments.