Again, all, thank you for your input. I feel a little embarassed because I feel like I came off sounding like I was a "wet-behind-the-ears" traveler. We often fly to Europe and the Middle East (well, Turkey, where my husband is from and where his family still is) and I've never encountered the prices I was seeing. I have almost always gone through the carrier themselves and have always gotten good deals (e.g. we went back to Turkey over Christmas using British Airways on-line, including a lay-over in London for about $500 per person). I was boggled by the prices I was seeing, assuming it was the >30 day return that was the problem.
Part of the problems I've encountered with the Expedias of travel booking is that sometimes you simply cannot change your ticket. If you do, the ticket is canceled and you have to buy a new ticket. That has happened to me once (with Orbitz, maybe??). Since our dates of departure and return are so, so unsure, I need something that's at least flexible (even a $200 change fee would be fine).
Anyway, I think I've already gotten the answer to my question from
michnic which is that YES, it's okay to buy a round trip ticket and not use the second half.
But really, thank bunches to the lot of you. Believe me, I'm gonna have a ton more questions before I get there, so please keep your advice coming. I do appreciate it all!!