heres a possibility.
get an inverex solar inverter. the cheapest one.
get a deep cycle battery. NOT regular truck battery.
I am using Daewoo DIB 225 for past 5 months with no problem so far. it has 1 year replacement warranty.
start using the ups.
after some time, you can add a solar panel to your system.
jinko, canadian solar, yingli are decent brands.
for your use, you can get 250 watt x 2 solar plates (mono crystalline)
in the cheapest solar inverter, the solar panel just charges the battery, or in the morning, when there is no light, the panel will charge battery and run your load simultaneously.
this will be the cheapest solution.
you must have shortest possible wire from your panel and battery to your UPS.