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.