Its available at betfair.

http://www.betfairpromo.com/betfairsp/prices/

Its interesting to note that SP prices will change as you add money to one side of the equation, similar to the totes. The more money you put on a selection to back it the lower the SP price will be when you start betting. The more you put on to lay the selection then the higher the final SP price will be.

Does anyone have anyway to work out the affect of a bet on SP before placing it ?

I am obviously not talking about $5 bets here but $1000+ bets/lays. I would be interested to see how others are handling it.