re: How much to save for a 2 week European vacation?

Definitely do open jaw. The convenience of not having to spend the time and money to get where you started is worth the increase in price. Plus you can just plan to finish where your flight is leaving from.

I recommend AirBNB if you are on the fence. Never had any issues and the places were all better than expected. We were staying in nice arse apartments/homes split a few ways for less than $60 a night. You can find some good stuff there under $200 that will be romantic as hell. That said, I would at least stay in a hotel a few times. It's nice to meet people or couples doing the same thing as you. The social aspect of hotels is what I missed when staying at AirBNB.

Don't know if you mentioned when going, but if you can avoid late April-Late July, you will save money. College kids traveling and demand increase price like crazy during those times.