We are listing all of the free activities around us for when my ILs come. It turns out that our budget didn't entirely pan out (works on paper, but people haven't paid us), and so we are a bit shy on cash. The ILs are super-cheap, so there's no way they would spot us on the holiday. I have the housing paid for, and gas and food are covered in the budget (with ILs paying half), so now it's a matter of activities.
Luckily, most of our activities were already free: te papa, play grounds, beach, hikes, botanical gardens, and various sites up the coast and such -- but several things cost $10-15/pp, and the ILs had plans like going to the zoo (where they would pay for themselves and possibly DS, but not for us -- which means I'll send Ryan but not go myself to save the cash . . .no, the ILs are NOT allowed around DS without supervision). And, DS wants to make cookies with his Mimi, so they'll be purchasing those supplies to do that and doing it in our kitchen, so that's relatively free, etc.
I have some other activities as well such as bowling (with coupon), and meals out (with coupons), and a coupon for some bike hire on the waterfront as well as one of those little paddle boat thingies. so, we can do various activities for very little money. The big spend might be Sommes Island with the City to Sea museum "fish and chips" tour -- which is * a lot * of fun. DH and I did it years ago and really enjoyed it. I think it's $20/person. And then there's the $20 tour of weta workshop as well -- which I think will send DS over the moon!
So, trying to keep it inexpensive.