Since UPS has to keep your PC running when there's a power loss, do you really want to cheap out on it? Keep in mind that if you want cheap and good UPS, you need to buy 2x UPSes; 1st the cheap one and 2nd the good one.
Also, as i said above, 1300VA UPS is more than enough for your PC. The 2500VA UPS you linked is overkill for your PC. And it doesn't end there, the 2500VA UPS you linked outputs simulated sine wave,
specs:
http://www.pceups.com/products/ups/line-interactive/m8
And when looking the OSes it's software supports, that UPS has quite an old design. Newest OS that UPS software supports is Win7. If you're running Win8.1 or Win10 (which you most likely are), you can't use that UPS'es software to monitor your UPS.
When looking for a UPS, there are 2 things to look out:
1. Output waveform (square wave, simulated sine wave and true/pure sine wave)
2. Design (stand-by, line-interactive and online)
From here you can read about the differences between output waveform,
link:
http://www.minutemanups.com/support/pwr_un10.php
And here are explanations about the UPS design,
stand-by:
http://www.pcguide.com/ref/power/ext/ups/typesStandby-c.html
line-interactive:
http://www.pcguide.com/ref/power/ext/ups/typesLineInt-c.html
online:
http://www.pcguide.com/ref/power/ext/ups/typesOnLine-c.html
Waveform and design
For PCs, line-interactive UPS would be more than enough since PSUs can easily handle the 2ms to 5ms transfer time of line-interactive UPS.
As far as output waveform goes, true/pure sine wave UPS is best used. While simulated sine wave UPSes are cheaper than true/pure sine wave UPSes, PSUs with Active PFC aren't compatible with simulated sine wave. You might get simulated sine wave UPS running with Active PFC PSU but there can be some major issues. Here's what, how and why.
How do you know which PSUs have Active PFC and which ones don't?
Simple, every PSU that has 80+ certification (e.g 80+ Bronze or 80+ Gold) has Active PFC.
What is Active PFC?
Further reading:
https://en.wikipedia.org/wiki/Power_factor#Power_factor_correction_(PFC)_in_non-linear_loads
What can happen when using simulated sine wave UPS with Active PFC PSU?
When simulated sine wave UPS switches over to the battery power, one of 3 things can happen:
1. UPS displays error resulting PC to shut down immediately.
2. UPS shuts down resulting PC to shut down immediately.
3. UPS switches to battery power resulting PC to power off from UPS (PC stays on).
Why it happens?
Simulated sine wave UPS produces a zero output state during the phase change cycle resulting in a power “gap”. This gap may cause power interruption for active PFC PSUs when switching from AC power output to simulated sine wave output (battery mode).
What to do next?
As stated above, your PC can run off from simulated sine wave UPS but be prepared when you face issues with it. When issues do rise, your best bet would be returning the simulated sine wave UPS and getting true/pure sine wave UPS. Or you can go with true/pure sine wave UPS off the bat.
Wattage
As far as UPS wattage goes, you need to consider the power draw of your PC and monitors. Maybe speakers and wi-fi router too if you plan to plug those into the UPS as well. Though, printers, scanners and other such hardware (full list on your UPS manual) don't plug to the UPS since their startup power draw is way too much for UPS to handle and you can fry your UPS.
Since your PC max power draw is 450W (GPU is 250W, rest of the system is about 200W), at least one monitor is added on top of it. Depending on the monitor size, they use between 23W to 52W. For more accurate power consumption, i need to know your monitor make and model so i can look up it's power consumption. Wi-fi routers don't consume much power. For example, my Cisco EPC3940L consumes 12V at 3A which means 36W.
This brings the total at around 550W, 600W if you also consider CPU/GPU OC. The 1300VA/ 780W UPS that i'm using would be more than enough for your PC as well.
If you want to run your PC off the grid for several hours (which also would explain why you want 2500+VA UPS), buy a gasoline/diesel powered generator and transformer. UPSes aren't designed to run PCs for several hours.