Please define "low cost" as a UPS can be $600 new in the box for a 2U on-line and that to me is low cost, great deal but to you it may be too expensive or maybe low cost to you is $1k?
Do you want line interactive or on-line?
Do you need metered outlets?
Do you need controllable outlets? (on/off/cycle)
Does it need to be silent? home use?
There are some $250 or less APC units on ebay that need new batteries, are not on-line, do no special 'features' but they "just work". I have 3 or so of those. I got a new in the box TrippLite On-Line for around $600 on amazon, again this was best 'bang for buck' some here don't like TrippLite but 10+ years protecting my house and we haven't lost equipment yet (we use other equipment from them too). I got some Liebert GTX3 off ebay for a couple hundred bucks which I think is a steal for a $1500+ on-line UPS.
Batteries are cheap on ebay and I've purchased 2 dozen in the last 2 years of varying brands and IMHO they are all the same other than the amp hours. They seem to come in 6ah to 12ah depending on specific battery size for your unit, and how much $$ you want to spend on getting the 'better' capacity battery. Often times I've found the AH rating to be 1 off, ie: 8 and 9 and keep in mind this isn't much but when you're using 3 or 4 batteries the capacity may add up to a whole other battery!
For capacity planning determine what you want it to do... being a home system I want longest run time because it will take me a few minutes to get generator power going. So I got the biggest storage capacity I could find, and in some cases add the extra 'pack' of batteries for longer run time. If you only have a couple systems it's not such a big deal.
Latest APC consumer/home don't seem to be using quality batteries like they did before
I've got a couple years on this system on my workstation with extra battery and if power goes out I have about 2hrs of using my desktop. If power goes out and I shut down and come back 12hrs later the batteries are already dead
ugh, hope to get another 10-15mo out of them.
I routinely use my battery backups so I never test them, so take that fwiw too.