Do your own ratings. For example the following will give you a good run for your money and may get a good pot if you can work out the right filters.

Consider win% multiplied by 2 and the place% for each horse. The basic rating for each horse is the highest of the two. e.g.

Horse 1 win%=22.5 place%=50, thus rating is 50 (45 compared with 50)
Horse 2 win %=33 place%=44, thus rating is 66
Horse 3 win%=19.6 place%=54, thus rating is 54

The top three of theses horses consistently win just under 50% of races so assuming the above examples represent the top three ratings come up with a price for each as follows:

Add ratings: 50+66+54=170 and find express each rating as a % of 170.
i.e. 29.4%, 38.8% and 31.8% respectively.

Now choose an overlay factor which is less than 50, say 40 and find 40% of each.

Your final percents would be 11.8%, 15.5% and 12.7%.

Divide each into 100 to get your final ratings as overlay prices,viz $8.47, $6.45 and $7.87 which should be rounded up to $8.50, $6.50 and $7.90

(Don't waste time trying to combine win% and place% as there is zero correlation between the two.)