I don't know where you are vacationing, but check to see if there is a place that rents cribs. We went to Florida this summer (near St. Augustine) and rented a crib. The cost was $15 a night or $65 a week. It was absolutely worth it. My daughter has never slept well in a pack 'n play and I was afraid that after a week in bed with us I would have to really fight to get her to sleep in her crib again. She slept fabulously in the rented crib.
Both sets of grandparents have bought cribs at garage sales and put new matresses in them so that when their grandchildren visit they have a comfortable place to sleep. I don't know if your parents have many grandchildren, but depending on how often you visit you may offer to reimburse them if they are able to do this.
Good Luck.
D.