Hi Zoe:
Sounds like a good trip. There is a lot of driving so I hope you like spending a lot of time in the car. Keep in mind that between points for most of your trip, there is not a lot to see and do. But it does look like a good mix of nature related activities with the glitz of LA, Vegas and NY thrown in. Also, I'm not sure when you are going but as pointed out before, this trip could be brutal if you do it in the middle of Summer.
Outside of the LA and Vegas, there are a lot of decent and inexpensive hotels and on your planned route they will be more decent than a lot of other places in the US. You could try Motel 6, Hampton Inn, Redroof Inn, Best Western, Holiday Inns, Marriott and Hiltons.
In LA, Phuckitman is right about the Beverly Garland. It is in the Valley which is north of LA but near Universal studios which has a theme park and Citiwalk which has restaurants, clubs and stores. It is pretty touristy though. The Beverly Garland was a Holiday Inn and they have a shuttle to Universal that I believe leaves every 30 mins. Universal also has a subway that will take you to Hollywood and Highland which is the middle of the tourist part of Hollywood. It has the Kodak Theatre where the Academy Awards are held and Graumans Chinese Theatre where a lot of premieres are held (I'm going to one there for The Rite next Wednesday). There are a lot of street performers - well not so much performers but characters. The Hollywood Roosevelt hotel is also there which is pricey but a good place to get a drink. There is a California Pizza Kitchen restuarant there that is reasonable and you can see the Hollywood sign from the front door. You would also want to walk on the beach boardwalk at Venice and look at all the crazy folks there and go over to Santa Monica and the Third Street Promenade and maybe Malibu and have drinks at a beach restaurant. And if you want to do a film studio tour, I can get you free tickets - just PM me. Also, some people like to go to Disneyland (like my kids) which is about an hour south of LA.
It's not as unsafe and as rude (ok maybe it is as rude) as people are telling you. But you should stay in the touristy areas and you will be fine. The West side and South Valley is generally safe. I'm in Westwood and have never had a problem.
As for Vegas, you will get the most bang for your buck for the hotel and food. Of course there are high end hotels and restaurants that are expensive but the middle of the road hotels and buffets are really a good deal, particluarly compared to Europe. And they are reasonable so long as you don't spend all your money on gambling or as they call it, gaming. If you stay any night other than Friday and Saturday, you can get some great room prices.
The drive down from Monterey on the Pacific Coast Highway is really a beautiful drive. You can stop in Carmel where Clint Eastwood was mayor, do the 17 mile drive at Pebble Beach and as you drive down, see Big Sur, Solvang a Danish village in the Southern wine region and Santa Barbara another beach community with wineries.
Hope you have a great trip.
Cotton