Welcome!
My family moved here to Southern Cal when I was 8 years old, and we have not looked back.
As you will be arriving in winter, I would urge you to consider the weather. Southern California, Arizona, New Mexico, southern Utah are popular winter destinations and have some amazing beauty. Florida is really nice and warm in winter, but very flat and (no offense, Florida lovers) generally uniform in scenery. Weather in the Northeast US is worse than England, colder in winter, HOT, muggy in summer. The northwest (OR, WA) isn't as bad, but it isn't particularly good either, maybe more like what you're used to.
December and January appear to be a good time of year to buy an RV, as buyers are scarce then.
In the US, you are quoted one price, but at the last step of the total calculation, a tax between about 4 and 10% is added as "sales tax". You can find what it is in each state online, and there may be small local variations. Oregon has no sales tax, as do a few other states, which could make a big difference. I'm sure registration tax varies too, but don't know about that.
A potentially more costly consideration is where you want to sightsee vs. where you buy the coach, considering an operating cost of $0.60 per mile or so. Fuel is delightfully cheap here compared with Europe, but it still adds up when you burn at RV rates. For example, if you want to end up in NY, it may be beneficial to start in Oregon, sweep down through California and across.
It is very easy to underestimate the size of this country. It takes some getting used to!
Best of luck!!
