I recently bought the GTDAudio G-380 4-mic wireless set from Amazon for about $140 shipped:
http://www.amazon.com/GTD-Audio-G-380H- ... B00HLVOO2GThey were so cheap that I wasn't expecting much, and the Amazon reviews were so glowing that I figured they had to be written by people being paid to write them or by people who don't really know what a decent mic sounds like. But I just used them for a long karaoke session and I'm completely blown away by how good they are. I tested them side by side with a good ol SM58 and they sound almost identical, to me at least. A common criticism of these mics is that you have to be really close to them and their sound drops off quickly as your mouth moves away, and in testing *maybe* I can notice that, but I sure couldn't notice it once we started singing. I wonder what a pro vocalist would say about them though.
The rack mounted base station is awesome too. Nice and solid and the independent level adjustment for each mic works beautifully. And the range is amazing: I tested up to a couple of hundred feet away and only got a couple of dropouts, even without the antennas extended. And when the range gets spotty it simply drops out to silence as opposed to getting staticy or making weird noises.
I had to change the batteries (two AA's) after about 4 hours on one of them, but I was using the crappy batteries that came with it. I'm hoping for slightly better battery life from name brand alkalines or lithiums.
Mine is the VHF version, which I've read may be susceptible to wireless interference, but I never heard a peep. If I was going to be using these professionally at a lot of different venues I'd probably get the UHF version just to be sure though:
http://www.amazon.com/gp/product/B00HLW1A5OI think the UHF model also lets you swap frequencies if you're getting interference.
I'm glad I got some colored windscreens to differentiate each mic, and to mask the dreaded and fairly strong "new mic smell". I bought these, which are cheap (50 cents each), but they're also a bit thinner than most mic windscreens I've used.
http://www.amazon.com/Bluecell-Purple-H ... B007E69TPABring a label maker and label each colored mic on the base station so you can easily turn people up/down.
Anyway, highly recommended. And it sure makes setup and takedown a whole lot easier.