A dog co-op is a good idea. Count me in. Years ago my mother belonged to a babysitting co-op and it worked out really well. The price of kennels has more than doubled since 2000-2002. I used to pay $12 per day for a miniature dachshund to stay overnight at a kennel in 2000. Now the same place wants $23/night + extra for meds and now I have two mini- doxies. With dogs, though, one might have to limit the co-op by dog size and/or temperament.

My friends all seem to rely on other friends or dogpark neighbors who also have dogs. Whoever is going away drops the dog off at the other friend's house. I guess that only works if everybody does not go away at the same time, as happens in late August. It wouldn't hurt to ask.
We were just talking about how we need someone who needs a dog sitter to let us crash at their place sometime soon, while our house gets some dusty renovation work done. But with 2 kids it's a hard sell.

someone really needs to set up a dogsitting coop for when people vacation. i just paid $500 to have someone take care of mine for 10 days, and that was cheap. Dirt cheap.