i dont think u can see other bidder's amount, it says ur bid is lower because someone has bid this number with amount higher than the amount u try to bid. 
but if u managed to bid it then someone overbid u, then u can see ur rank.

not sure, but after placing bid can see only ur own ranking, example in screenshot.
so my rank is 7, if not mistaken, it means there are 6 people placed higher bid than me after i placed my bid.

Keep trial-and-error to put some figures.
E.g. put RM400 bid on a number you want, if system says your bid is low, add another RM100, maybe you can proceed to the payment page now, but you are free to cancel the bidding without placing the bid amount. You can lower the bid amount again to guess/see what's the current highest bid amount.

I've tried this for 2 numbers I wanted to see how's the current highest bid now, both already exceeded rm500, so i'm giving up.