Have you had a look on eBay? You might be able to pick up a second hand one there. I'd be inclined to stick to a proper Apple charger, just because of the scare stories you hear about exploding laptops and iPhones when the wrong chargers are used. Also make sure that it's the right voltage - don't buy a US plug if you are in the UK (and any knock off chargers are unlikely to be for our voltage as the market wouldn't be big enough to justify making it).
Qualcomm Snapdragon 835 benchmarks: Antutu, Geekbench 4, GFXBench and PCMark results