Popups are very expensive. They have the same needs for a fridge, furnace, holding tanks, toilet, lighting, fans, and other items and also need a lift mechanism and special sealing between the base and top units.
Want to save money, buy a used hard side camper. A Lance that sold for $18,000 in 2008 can be bought used for $12,000 and the same model or comparable model bought today sells for over $35,000.
You can also save by getting a camper that does not have a bathroom but I would not recommend it. It is also a problem with a popup as you need to raise the top anytime that you want to use the toilet and the toilet will be a cassette type instead of a flushing toilet with a holding tank.
The advantages of popups are a lower center of gravity, lesser weight so they can be used on 1/2 ton pickups, and a lot less air drag when driving down the highway.
You get twice the value with a small travel trailer that is 24 feet or shorter as compared to a camper and do not need a heavy duty truck and its expense.