Hi @Misi0.
I know nothing of the Western Cape, South Africa STR market, so your intensive personal research, is needed here, as well as any input from other SA hosts.
I use to have about 150GB per month here in Oz per month. That was dramatically consumed depending on the guests. For us, we may be the first opportunity for photo uploads etc. Also remember, data is quickly consumed if a guest connects for gaming.
I decided a couple of years ago, if I was serious about offering wifi, then I needed an unlimited plan. You can’t have lots for one and nothing for another.
Mostly, consider your pricing and absorb the costs within your daily rates, and remember, it is a tax expense.
Noting: a slow internet system will not assist you with positive reviews.