I wouldn't say it's a fair comparison personally. There's a reason why Optus can offer more for less, they've got more people willing to pay an amount for a popular sport and will gain a lot more in sponsorship than BSN could ever wish to.
Speedway is such a niche sport. You're not going to get anyone other than speedway fans willing to pay to watch a live stream and as a smaller venture BSN I'd doubt they'd have the pockets to operate at a loss.
The fairest comparison in my eyes to speedway in the UK is ice hockey, although attedance wise ice hockey does tend to garner more interest in the top league, but much like speedway in this country it is a niche product- amongst every side in the EIHL they all offer live streams of their matches and you won't find a single team offering anything below £15 per match.
So it lines up just about right imo and I think it's a fair price for what's on offer- ultimately if you bring down the cost by £2-3 it's not really enough to entice new customers. Bring it down by £5 and yes, I think you'd get a lot more viewers and people willing to buy in, but you'd also devalue the live expirence and would see a lot less people showing up for the meeting in person which actively needs to be avoided.