I'd recommend a small powered speaker. That way you don't need a separate amp. I have a JBL Eon10 which is just perfect for a smaller venue, and fairly light weight to carry around. You can buy one new for about $400, but try Craig's List or EBay - I picked one up for half price, in very good condition.

Then get a good quality mic. The standard is the Shure SM58 for $99 - the price never goes below that. But for a little more try the Audix OM5. I just got one for $139 (before the price went up) and it's very nice, a step up from the SM58.

With the JBL powered speaker you can input a condenser mic directly with it's own gain control and preamp. But if you want to use two or more mics, a small mixing board would be a good investment. And that's about all you need.

Cheers, S. in Seattle