There are several way's you could go about this....

1. you could get a powered mixer to run your mains, and a separate power amp for your monitors.

2. you could get an unpowered mixer and a couple of power amps to run everything.

The later is better, but the first might be more convenient.

Most 200+ capacity venues will have their own PA system, but some might not. A huge amount will depend on how much you are willing to spend. Decent PA's can get expensive quick! If you're going to be running the bass and drums through the PA, you'll definitely want to get at least 2 sub cabinets, along with the mains.

Here are a few examples of setups for you to look through:

Yamaha EMX512SC 8-channel powered mixer running two JBL JRX125 speaker cabinets

Add a power amp like a Peavey PV 900 and a couple of floor monitors, and you're set. The JBL's will carry the bass and drums ok, but they will be a bit week, and might muddy up the vocals a bit.

A better setup (more money) would be something like this:

Peavey PV14 mixer, Peavey PV 2600 power amp running 2 Peavey SP 2 cabs. A Crown CE4000 power amp running 2 Peavey SP 218 subwoofers. You would also need another power amp and a couple of monitors (like mentioned above). Then you would want to get a crossover to route the signals, such as the dbx DriveRack processor. You can definately get cheaper than that, but it does have a lot of nice features for getting things to sound right. Also, don't forget about mic's, mic stands, and cables.

As you can see, it will largely depend on how much you have to spend.