I can get the Ns-Ap2600 set (2+2+center) for 80 dollars to my door. The four "linaei" should bring just about that. I have to admit I like the idea of everything matching and knowing that the sub and surrounds were "made for each other". aka voice matched, the surrounds frequency range meets right at the sub's cutoff of 90hz.
Subwoofers are not "voice matched" to the mains. They are reproducing different frequencies, so they always sound different from the main speakers. So there is zero need to get a "matching" subwoofer for the main speakers. It just needs to go high enough so that there won't be a gap in frequencies between it and the main speakers. Normally, if people go astray here, it is that they don't get main speakers that can go low enough, as it is not a good idea to have the subwoofer reproduce very high frequencies.
Also, although it is a very good idea to have matching speakers across the front (because when a sound pans across the front three channels, it is good if it has the same tonal quality while being reproduced by the different front speakers), it is far less important for the rears to match the front. Simply put, you do not hear as well things that are behind you as things in front (which explains why, even in the dark, in order to listen to something carefully, one turns to face it; people who are blind from birth also turn to face things when they want to listen intently, because one's ears are aimed for forward listening), so the rear speakers matter less. Also, typically, the types of sounds recorded for the rear channels are "ambience", whereas the main sounds, such as the dialog, may come from any of the front speakers, as, for example, if a person is on the far right of the screen, they may be speaking from the right channel speaker.
My advice is to keep what you have, and in the future, if you can afford it, try to pick up another speaker like what you have for completing the 5 channels. And whenever you have money for it later, add a subwoofer; I recommend SVS, if you can ever afford one.