First You should apply Saudi Embassy for Visa thru any of the Hajj and Umrah Agent, I would suggest going by Agent's transport (buses are nice and comfortable) or else it is about 18 hours driving with stoppages for food and prayers intervals, once u cross Salwa border roads are big and road signs will lead u to Makkah straight, but I thinks ur already late for going by ur car now, after Ramadan the Umrah visa is not available until one month after Hajj
good luck