On the left hand side of every page is the RTA fuel cost calculator that will help work out the cost of gas for your vehicle, which after all is a major expense on a trip of this length. Here, you will find more budgeting tips to help you work out your expenses. You should also invest in making sure your vehicle is fully serviced and completely checked over before the trip as well as having some kind of emergency fund for unexpected repairs while on the road.
Use the search button to explore the forums and you will find loads of useful info to help you get started. I am not sure that Tijuana is worth such a big detour especially with the troubles near the border I keep hearing about.