What are good, cheap Monitors, Alesis anyone, Monitors Options

I am setting up a home based recording studio. I need to get some cost effective monitors. We are going to be using a Motu 828, and eventually will be mixing surround, so we'll need 5 monitors, thus the reason for cost effective, we can't pay $1000 for each.

To start out though, we will be doing some voice over work as well as some vocals, and making an album or two.

Any thoughts on what might be a good monitor? What about the Alesis MKII active, they are $450 a pair, and are Bi-amped? Any one use them, are they any good?

What else would you recommend?

Also, if I move on to surround mixing, can I use the Alesis as the two rears, and get three more that are matched for the front, left and right. Or do all 5 need to be matched? How important is it that all 5 are matched?

Thanks for the help and suggestions,

Greg