Hidden road

In the Salvage Wasteland track go by gate # 2 where the ramp leads into the middle of the track, use the dirt on the opposite side of the ramp to get over the fence, once u are on the other side of the fence drive around the track to the opposite side of the track, once there you should be able to see the road.

Hidden money

On the Farm Road track, go under the train trestle in the middle of the pond to find $1500

On the Restricted Area track, go straight when you pass through gate 5. After a little driving you will reach an aircraft hanger with a jet inside. In the corner of the hanger is a chest of cash

On the Laguna Del Ray track, off on the right is a small island just offshore. On top the island is a chest of cash

Between gate 6 and 7 on the Black Gold track is a fenced-in area that contains another box of cash. There is an oil truck nearby it

When starting on the Treasure Bay track, go over to the beached tanker boat to the right, and drive around on the water side. You can find a chest in the side hull, with $666.

On the Truck Stop 101 track, go to the "hidden" highway and drive alongside the right side of the road. You will eventually find a chest of cash