Okay, online UPS and double conversion UPS are pretty much functionally equivalent terms, and checking I do see APC models ranging from about $250 to $750 depending on rated output. A 1000 va (600 watt) model is $257 on Amazon (and at rated capacity has a run time of 6 minutes). So I guess the online versions are working their way into the consumer market. Been a few years since I looked seriously at that capability, and the last "big" UPS I dealt with was a multi-KW model designed to run an entire server room, and had about 24 hours of battery on it (no generator was available at that location at that time).
My personal opinion is that a UPS should have at least 20 minutes of battery run-time (which typically means you have to get a unit rated somewhat higher than your actual power draw), as it will take that long to either do a graceful shutdown of everything running on UPS, or switch it all over to generator. In a consumer/home environment, that typically means going around to more than one location (item running on UPS) to do the shutdown or switch over, and 20 minutes is pushing it (unless you have a whole-home auto start generator).
The one I've had since '99 or so is 1000 VA, and while I don't remember its exact cost, it was probably at or less than that $257 mark then (I certainly wouldn't have been willing to spend a whole lot more than that amount) so they've been in the consumer market for a while, depending on how you define "consumer market". I think back then the SmartUPS line was intended for workgroup servers moreso than homes (maybe that's still true)
The rated 6 minute runtime isn't a problem unless you really pull 600 watts. Today my PC, modem, switch, wireless router and 27" monitor total just over 100 watts, so I've got a pretty decent runtime. Back when I bought it I think I sized it for 2x my normal draw, wanting to get 10-15 minutes out of it. PCs have become much more power efficient, and the 20" LCD I bought back then (for $1200...yikes!) drew about 60 watts by itself IIRC.
Since I don't have a generator, the UPS is just for convenience to avoid a momentary power blip from causing data loss. My PC will automatically shut itself down if the power goes out and the battery gets low, so I don't need to do it manually. I have a smaller UPS for my Tivo, but I don't bother to shut it down. It handles power loss just fine, the only thing I'd care about there is not losing a recording but the power goes out for my entire neighborhood my cable will go with it anyway so a longer runtime for the Tivo doesn't help much.
SL5, PI-6S, SA-6AL 3xSWM16, 21 H20-100, 1 H20-600, 7 H24-700/AM21