Or... check your airline's rules.
Buy a round trip ticket with any return date that gives you the best rate for now. Then, call them once you're here & tell them you want to change the date, but you're not sure for when.
At least with American Airlines, I've been able to indefinitely postpone my returns. I pay a change fee (most recently it was US$100 i think) + any difference in the actual flight rate when I finally choose a return date. At times, I've only had to pay the change fee. At other times, up to $150 more in flight differential. I think with AA the ticket/return can be postponed for up to a year. Just keep your booking/reference # for when you're ready to finally pick your return date.
