I'm heading off to Europe for 6 weeks (mostly work, then a big of vacation). I figure:
-1k for the flights
-1k for the first month accomodations (long term stay)
-1k for the first month food/entertainment (basically 30 bucks a day to eat out, with some days eating cheap from the grocery store, and drinks are cheap so don't need to blow a ton going out)
-Then for the last 2 weeks of vacation, can probably hostel it for ~30 bucks a night (so, say 450). Probably 40 bucks a day for food (600), another 25-30 bucks a day for tourist stuff (350), and then say another 300 for trains/flights between cities. Maybe a few hundred more in incidentals (daytrip tours, or shopping, or other splurges)
So, all in all, probably going to be about 5k total for a 5 week trip, although the 5 week business portion of the trip will probably be cheaper overall than 2 weeks of travelling (especially since flights and hotels for the business trip get reimbursed/deducted). But yeah, obviously when you're travelling with a family, you can't stay in a 20$ a night hostel, and it's very easy to add up if you eat out at nicer places, spend more for airfare, check bags, go on more tours, etc... And obviously depends where you go - as mentioned, the US is pretty damned expensive, but if you're going through, say, eastern Europe, it can be damned cheap. When you're getting a full meal with a beer in a nice restaurant for about 10 euro, that's so damned nice.