But yes, I understand your situation especially since there's a 20$ wagering requirement, it's 50/50 chance that you will be able to profit from it or lose your money just to complete the wagering requirement. It happened to me the first time I joined, my 20$ becomes $10 and I only got lucky to win another $18 in my combo boost.
I don’t really follow this event because I don’t actively bet on sports. However, if i read the rules there is mentioned as
“no restrictions on wagers”, I think it will be easier to meet the requirement if combined with wagers from slots (CMIIW). As we know, slots have a faster method for reaching the wager requirement, even with low bets. if the rules really able to combine, and participants want the smallest bet every spins, they can bet on Pragmatic slots with IDR currency balance setting.

Since Vega is available in IDR denominations, players can place a minimum bet just IDR 500 or $0.028, this is better than using dollar denomination because the minimum bet slightly more expensive.
just let me know if i'm wrong with that rules
As to what I have observed from other participants, most of them seems to complete the wagering requirement by purchasing the Buy Bonus in slots. The same as you think, it's the easiest way to complete the wager requirement. Mostly in USDT, so I am not really sure if using IDR is fine. But since the rules stated that "no restrictions on wager", it should be included.
Choosing a game always depends on you, whether you take it slow, or finish it as soon as possible.