How serious are you about getting your band off the ground ?

If the answer is very, I'd sort your selves out with a second hand ~1k PA Rig for vocals and backing vocals.

You will need:

1x1k power amp (or 2x500W, one for the left channel one for the right channel)
A big EQ (optional)
An effects unit (very old and cheep, this is to add a little echo)
A 4 or 6 channel desk
3 or 4 Shure SM57s
Cheep mic cable (about 30ft x number of mics)
2 monitor wedges (this is optional but also a good idea)
L and R speaker stacks (capable of about 750-1000 W each)
Lots of speaker cable
Some sort of road case for all your amps and electronics

Next you need a wiling friend to do your sound and a place where you can make a lot of noise with out getting arrested. Then you need to set it all up and practice like crazy.

If you are going to do 2 nights a week practice and one or two nights a week gigging, it is going to be more expensive hiring a PA than buying a second hand one. You can also open up a side line in hiring it out to other bands.

As your band progresses you will play more and more venues with there own house PA, at which point you only need to use your one for practice and hiring out to other bands. It is still a very good investment.