A woman I work with, her son, just turned 40 last weekend & his wife threw a surprise party. They rented a Knights of Columbus Hall (not the nicest halls, but cheap), had most of the guests bring a dish (salads, meatballs, dips…), and ordered pizzas. They were able to purchase a keg from the hall and they bought all the decorations. Maybe you could do something like this without breaking the bank? And the mess is not at your house. Use disposable everything, so it ALL goes right in the trash before you leave.
Or rent a room at a local bar….maybe one that has things like pool, darts and video golf. This way people can have an activity or just hang out. I would order the food or munchies for people and MAYBE buy everyone a round of drinks…after that, they are on their own for drinks.
Know anyone in the Limo business? Maybe you can rent a limo and do dinner and drinks with friends and no one has to drive? That's always fun, but the Limo can be pricey.
Last thought…find something special to do in Sequoia for just the two of you. Arrange for your mother in law to watch your daughter and surprise him with a night out on the town. With just the 2 of you, it should not cost that much. Having said this, I have no idea where Sequoia is or what there may be to do around there, but hopefully you can find something.