Dont use this boat ramp, its very slippery and theres the hidden bonus of bumping into a dumped car in the river or stepping on a syringe !, and most of the way down to Alfords point is 4 or 8 knot zones which can be painfull !
As previously suggested if your comign form Winston Hills put in at Georges National Park at Revesby, it will cost ya $7 but the ramp and parking is much better, and from there you are only 20 mins or so from Botany Bay if you wish to venture that far down !