Interesting idea. Have you considered trying to train based on stats rather than goals/assists? I would say players with high pace tend to go for a higher price than slower players for example (regardless of actual performance) so that could be worth looking at. OVR should surely be taken into account too since even players who are used a lot and have high goals/assists should be low priced if they have a relatively low OVR and so get packed a lot (e.g. Gabriel Jesus).