And looking into it some more, whilst trying to get the budget down I'm considering dropping San Antonio and Buffalo/Niagra Falls.
Dropping Texas would leave a lot in central US to visit if we ever did this again. And the Niagra Falls could go into the future Canada trip I guess.
This, along with reducing accommodation costs and limiting our daily food spend to £60/$90 a day between us, roughly gets us in budget of around £5,500. Not including £2000 for spending money (attractions/shopping).
Does this sound reasonable at all? In favour of leaving out TX and Niagra Falls?
This change sounds like a reasonable solution to saving time and money and still seeing some of the better areas of North America. Your original plan would probably have cost a lot more than your budget allowed. It is expensive to visit the USA. As you have left Canada out of your trip, you can always make that a future trip. If you plan to do another trip in central US, you should consider seeing Chicago. Chicago is also a great city for foodies.
Good luck and enjoy your trip.
Car rental can be very cheap check out Priceline and also Priceline is good for bidding and getting good deals on hotels. Look up couch surfing and consider joining, not so much for free accommodation but for the rich cultural experience and also check out Amtrak as it can be relaxing and reasonable to travel by train. I love San Francisco and Yellowstone is stunning as is the drive from Yellowstone to Cody Wyoming for example. Vegas is a spectacle, close to Grand Canyon.
You could fly into San Francisco and home from New York. You could fly from Vegas to New York there are some good seat sales maybe not as good as Ryanair though. Niagra Falls is worth seeing and if you love good food then Quebec City is both charming and offers up the best food I have enjoyed as a tourist and yes I have been to Paris, so that is my two bits worth enjoy your trip you cannot see everything but you can get an impression once you choose what places resonate the most with you in case you only come this way once - pick your highlights and plan your route and if possible allow a little room for flexibility.
[ Edit: Edited on 15-Sep-2015, at 18:17 by CherylGypsyRose ]