or you have to buy a $400 speaker set that does a fantastic job!
Well, considering quality home theater speakers can easily cost well over $1000 for one speaker, some may argue your point about a whole $400 "set" doing a fantastic job.
That said, yes, you can use a home theater set of speakers with your computer. But note most home theater speakers do NOT have built in amplifiers as nearly all computer speakers do. If your speakers have built-in amps, then you should be able to use the line out jacks of your sound card or the motherboard's integrated sound, if your card (or motherboard) has the necessary outputs. If your speakers are not self-powered, then you need to come out of your sound card through the "line-out" jacks and into a home theater amplifier/receiver that your speakers then attach to. Or your sound card may provide a digital/optical out that your speaker set may support.
As for those $80 speakers, they will not provide thunderous bass or LFEs, extreme highs, nor distortion free in-betweens that a decent set of speakers will. Fidelity is not about power. But for the price, they will allow you to enjoy the movie in surround sound.