We only go to the USA if plane tickets are already paid (sponsors, labels...). In fact, we're looking for support in NYC and LA and everywhere to play soon because we have our flight tickets paid this year.
Here in EU, earning money from gigs is getting more and more difficult but, if you got flights solved, then everything is easier: As someone said before, ask for spot to sleep, dinner and gasmoney from tickets and MAYBE you won't spend a real lot of money.
Try to book dates as close as possible in time and space.
Money per day (minimum): Van: €150, gas: €50, food/drink: €100 (breakfst, lunch, etc). add up flights, promo, some sleep in hostels, and you have €500 daily.
Of course you can make it half cheaper if you find a friend's van and you got your flights paid, so move out for sponsors: they can advertise in your posters, net promo, banners at shows... We often try to get sponsored by hotels to get our sleep paid (and in great conditions).
hope it is useful for yer band!