I had been watching this site for a long time without registration. We got a lot of valuable information, and now it is my turn for contributions.

We are a family of 5 (including grandpa, grandma, a 3 yr old), living in San Francisco Bay area. Before our travel, we try to weigh the cost and fun between cruise and RV trip. For a 12 days travel, the best deal I can find for cruise is 1100$/person plus some hidden cost such as Shore Excursions, Tipping etc. In this aspect, RV trip is much more affordable. On the other hand, Cruise is much more relaxing, but it can be boring to stay on cruise for that many days and sleep in an interior windowless room.

Summary of our cost:
1. Rental fee for a standard size Class C RV:
We use Cruise America RV rental, which is109$/day with insurance included for 13 days = $1417. Our travel is actually 12 days, but we have to rent an extra night as they have the rule that RV must be returned before 11am.
2. RV mileage cost:
0.32 /mile. We drive 2399 miles in total As we got the deal with 100miles/day is included in the RV rental fee. the total cost for mileage is (2399-1300)*0.32 = $351.68
3. Gas
Total Gas bill is 993$ with average gas price is $3.7-$3.9/gallon. We use 263 Gallon Gas in total, So the RV Gas consumption is about 9mpg which is common for standard size Class C RV.
4. RV park/campground
We stay 12 nights on the RV, The RV park/campground fee total at 384$. The parks ranged from dry camp at $20-$25/night to $60/night full hookup one at Grand Teton national park. We use an Android App named RV Camps Locator. In comparison to Reserve America, this app contains much more RV parks,actually, the most complete one I have seen so far. It map out all of them and is really helpful to locate RV park on our way. We can decide how much we want to drive each day with great flexibility.
5. Dining
We only eat out twice - 140$ in total. We cook on our RV or campfire all the other time. The saving is extraordinary for 5 people. The refrigerator is kind of small, so we bring a large cooler with us. It is very helpful to have a meal plan for everyday.

The total cost is less than $3500 and the trip is well worthy. It is our first time to drive RV, surprisingly, it is not hard to drive at all, just as easy as driving a Van. The only part tricky is when you back your RV, you would need another person to watch it for you.