I have two IKEA smastad loft beds with desk and wardrobe attached. These beds cost 850 new and if you want the mattresses which are in good condition and have no cooties, you can have those too.
They are great beds and only a few years old, but we are moving to a place with lower ceilings. Taking the beds apart and getting them out of my house is the hard part, and the price reflects that if you want one of these beds, you need to come do that. I have the original plans and it can be done with basic tools, but breaking it down and moving it is a bit of a challenge, but, for the right person, a little elbow grease and a small amount of cash can get you some great new beds for your kids. They really feel like they double the size of a small bedroom.
https://www.ikea.com/us/en/p/smastad-loft-bed-white-blue-with-desk-with-4-drawers-s99557698/