Yes, the prices on the exchange and S.P. are almost identical.

However, on S.P. the horse is layed on liability.

If a horse's price is $10 it can be layed on the exchange for the minimum of $5 which means that if it wins the race the layer pays $45 to the backer.

However, on S.P. it can be layed for the minimum of $30. If the horse is beaten the layer gets about $3 ($30 divided by 10) from the backer, and if it's price is $300 the layer wins about $0.10 from a lay-bet of $30 ($300 divided by 30) but he can only lose the outlay of $30.

In other words, the layer nominates how much he can lose on S.P but on the exchange he nominates how much he can win.

If one is not familiar with laying S.P. it can at first be quite complicated.