phLOx

I agree with all of the posters here re running DC products on DC power.
I'm in the router industry we are one of the distributors for things like TP-LINK, Mikrotik, Ubiquiti etc... so I can confidently say I know the stuff well
Your best bet from a price / performance point of view is to get a 12v battery and charger and then run all of the 12V stuff directly off the battery, for other voltages get step up or step down converters, these are quite cheap and readily available.
I have around 120ah worth of batteries which run 4 routers, my home automation Intel NUC (have a step up to 19v for this although it does run off 12v but I've done this more for power filtering), efergy energy monitor, fibre router, 2 x outdoor routers for a ptp link,  it is capable of keeping this equipment up for days.
Most routers are either 9V or 12V, the 9V routers can almost all run at 12V without issue, products like Mikrotik have a very broad input voltage range of anywhere between 9v and 56v so can run on a plethora of battery configurations.
Its not a good idea to increase the capacity of the UPS you will have charge & heat issues they are not built to be expanded (well not the small entry level units), UPS in general are not designed for this type of work, they are designed to keep things like PC's powered up until a generator / inverter kicks in not to power a host of devices for hours. Unfortunately this is the perception and tons of people are rushing out and buying UPS' to act as inverters and with the frequency and level of load shedding we're faced with it is damaging the UPS and they're not even seeing their 1 year warranties out.
I'm happy to share pics of my setup and offer advise, I've been running on batteries for over 10 years with no issues. 
 

I would say it is worth it. Just the cost of your time (to go out and buy a new battery when it fails) will possibly exceed that R200 easily 🙂
 

Your Mecer UPS has a built in inverter. The term UPS doesn't specify any particular technology but has become the name given to an inverter UPS.
To differentiate these DC UPS's (i.e. that don't generate 220V AC)  are being referred to as a 'Mini UPS'