I bought a Roomba (It cost somewhere around $800) for my parents. They generally spend most of their time on the first floor, and the Roomba just stays upstairs. It gets itself stuck sometimes (mostly because my mom hasn’t Roomba-proofed the space—clutter under some of the beds) but she is always shocked to see how much dirt it picks up despite how little use the space gets.
It’s not a miracle worker. It doesn’t really deep clean like a high-end full-sized vacuum. What it excels at though is keeping up with the surface dirt on a regular basis, minimizing the dust in your house and making your life easier. The Roomba never gets tired, or lazy. If it’s not stuck somewhere, it will complete it’s cleaning every time it’s scheduled to do so (which is a lot more impressive than my track record).
It’s been several years now and I think they’re really happy with it for what they use it for. If guests are going to come stay in the upstairs guest room, my mom will still pull out the regular vacuum, but otherwise she never has to worry about lugging it up the stairs.