Any other solution is really going to cost you because you’ll be paying for gas + convenience + repositioning of a person and/or a vehicle + someone’s else’s time.

I’d be happy to give you a bid if you’re on the Wasatch Front.

But your cheapest way will definitely be to use the pickup truck/SUV you have (or that you rented for the weekend) to pull a UHaul trailer, and just make a weekend out of it.

Your second cheapest option will be to figure out what you would be willing to pay, and Venmo that amount + whatever you’re able to get for the furniture on Facebook Marketplace to your SIL.