Last year I found a pool on craigslist for $50. It was a 3 ft deep by 10ft diameter. We bought that pool and it has been the greatest source of fun for our children. They LOVE it. They get in there and splash and laugh and play. I LOVE it.
We also got a camper that has just brought countless moments of joy. The kids actually said they prefer the camper to a condo at the beach. :) at the campgrounds they run, ride bikes, play ball, swim and just have a great time being with family and being kids.
If I can get you to do one thing this summer take some time, even if it is one night and just spend it enjoying time with your precious children. They are growing up right before our eyes. ENJOY it. :)