Lots of the industrial units charge £5, there is also some free street parking if you get there before 1pm. Come off the M5, but head towards the town in the opposite direction to the Hawthorns, go 75/100m and turn left, the area is mainly small industrial units. I seem to remember a petrol station at the junction of the turn into the area. Its about 12 to 15 minutes walk to the ground. You walk over the M5.
On Public transport there is a Wolverhamption tram from Grand Central (Birmingham New Street Station) with a stop station called Hawthorns which is close to the away end.