We stayed with MiL and her partner for 3 months on arrival, and bless 'em they're fabulous but I think that was long enough for all of us
My parents will visit for 2-3 months at the end of this year *eek*
At MiL's, we paid for each alternate week's food shop and a bought a little extra, filled their car if we borrowed it, did laundry and cleaning as needed, hubby did some DIY-fixit etc. I hope that my parents will mostly do the same (as well as, um, occasionally go someplace else for a couple of weeks..).
I know flights are expensive, but at the same time if they'd flown anywhere else they would have had to pay for accommodation as well as food, let alone transport, and even when the NZD is strong, the exchange rate ain't bad.. (for holidaymakers anyway).