There’s no clear cut answer to this and of course it depends on how long you plan to travel for. However, the total cost for your road trip can be broken down into 6 main considerations: flights (if you live outside the US), car-hire, accommodation, fuel, dining and entrance fees. Remember - it’s better to over-budget and have some cash to return home with than to under-budget and have to curtail the fun!
Flights (if needed) could be a sizeable chunk of your budget and you should shop around, the earlier the better. Web sites such as Opodo and Orbitz are a good starting point.
A good starting point for car rental (and I’ve always found the cheapest) is CarHire3000. The cost incurred will be affected by the size of the vehicle, the insurance offered, and whether you will be required to pay a one-way (or drop-off) fee. As an example, a 4 door medium sized vehicle driven by a 25 year old for 2 weeks in the summer can be approximately $650 including all insurances but not including a one-way fee. The one-way fee (picking up at Chicago and dropping off at LA) can be approximately $200. A good tip is to request a quote online and hold off responding for a few weeks. You’ll then be emailed a small discount offer to entice you back.
The cost of accommodation varies according to quality and whether you have opted for chains or independent motels/hotels. In the summer, certain budget motels offer rooms from $40 which will be more than adequate for most peoples needs. Allowing $50 to $70 a night for a double room should cover most of the motels you’ll encounter. Prices in the larger cities or for classic/vintage Route 66 motels might be a little more. For the vintage motels it would be highly recommended to reserve a room in advance.
A good estimate for fuel costs can be obtained using the fuel-cost calculator found here. An estimate of $250-300 would be realistic for an average sized family vehicle.
Eating on the road can be fairly inexpensive (particularly if you’re from Europe). Breakfast or lunch at a small diner could cost from only $5 per person while an evening meal might cost in the region of $10 to $20. A quality steak at the Big Texan Steak Ranch can cost less than $20 or you can opt for their whopping 72oz steak - eat it in less than an hour and it’s free! Don’t forget to budget approximately 15% for tips.
Entrance fees to small museums and attractions generally only come to a few dollars if not free so that just leaves the national parks or larger privately owned attractions. As a guide the National Cowboy and Western Museum charges $12.50 for adults whereas the Meteor Crater admission is $15 per adult.
