Cheapest Surround Sound on Xbox 360

Hi guys.

I am looking to get some kind of 5.1 surround sound on my xbox 360. I know very little about audio systems, but from the research i've done it looks kind of expensive.

the most obvious solution i can see would be to buy a surround sound system with receiver that has an optical in. that (at least the ones i can find) is more than i can spend at the moment.

i see that logitech has some PC 5.1 speaker systems, but using those with the adapter wouldn't be really be 5.1, it would basically be just 2 speakers.

my question for you guys is what is the least expensive way I can get a 5.1 system going for my 360? i dont care if it's digital or analog, just so long as there is surround sound coming through 5.1 speakers.

the tv i'm using is a Vizio 27" LED, so I'm using HDMI for my video. the tv doesn't have spdif out, or output for rear speakers.

i read something about someone using their PC's sound card to decode the audio, i don't currently have a 5.1 sound card in my system, but if purchasing that and speakers is the least expensive option, i'm fine to go with that.

I was looking at walmart's website and i see "surround sound home theater systems" for only like 50 bucks, but as far as i can tell they only output surround sound for the included dvd player.

i'm willing to go with any option, however it has to be rigged, to get some surround sound going for my 360.

any help would be appreciated.