How to handle salary negotiations while negotiating a postdoc position?
I think all your concerns are very reasonable. Honestly, I am not really buying into the "money is no concern in academic job hunts" story. A postdoc is a job. Part of a job is a salary. I never understood why you are allowed to ask about housing, students, packages, whatever, but not what money you are going to make.


  Q1: how can I inquire about the salary offer/negotiation without appearing greedy or money-oriented?


In the past, I have brought up this topic during my faculty visits (i.e., when they invited me over). At this point, nothing is promised yet, but it should be reasonably clear that both sides are interested and will not be scared away by trivialities. That is, if the PI went through the pain and costs to fly you over, (s)he isn't going to drop you just because you said the nasty M-word. Also, a slightly uncomfortable topic is better discussed face-to-face, over coffee.

Usually, there is a point in the conversation where you can drop it in without being overly heavy-handed. Don't make it the first thing you ask, but some time during the day quite naturally the formalities of your employment will come up. At this time you just ask directly for your yearly salary.

"You say that my employment would be full-time for 2 years? By the way, how much in yearly salary would this roughly amount to?"

If this is above what you expect, nod sagely and let the topic go. If this is slightly below your expectations, ask if there is possibility to increase (e.g., with additional teaching, by bringing in grants). I wouldn't really consider this negotiating (as they like to say over at Workplace.SE, one cannot negotiate without being prepared to walk away), but rather an open discussion what you would need to do to get to your expected salary. If the offer is way below your expectations, to the extent that your standard-of-living would actually unreasonably sink from your current position, explicitly say so.

However, keep in mind that there is a good chance that in this third case, you may well have an unfixable problem - likely, the PI will be unable and unwilling to go up very far from whatever (s)he currently has in mind, so there is a good chance to you will either have to take the lower salary for the experience, or be prepared to walk away. However, at least then you know - this is still much better than finding out when you are already in the US that your salary isn't close to what you are used to.

Edit:
There is, unfortunately, also the very real chance that the answer will be something evasive, for instance:


"We'll tackle this when you are here, ok?"
"Salary will follow the university standards / NSF standards / whatever."
"I don't know from the top of my head, but I am sure we will be able to figure it out."
...


If this is the annoying case, I would press the topic. Really. No matter what anybody says, it is not unreasonable to expect to have more or less exact knowledge about salary before agreeing to changing jobs, especially but not only if that "changing jobs" will mean that you move to a different continent. Also, it is a super-bad sign if the PI won't even give you a ballpark number. That alone would make me very anxious about the entire salary topic.


  Q2: As a follow up, is it reasonable to expect/ask them to match my current living standard?


Partially. Your current standard of living isn't really of much concern to your new employer, but of course you can use this argument to plausibly explain why you care about having a specific minimal salary goal. Of course for the PI it's not an ethical problem at all to respond with "I don't have this money", or "For this money I can get two qualified people who don't have your expectations regarding standard-of-living". So I certainly wouldn't expect them to match your current salary, but it is not unreasonable to ask for this.