I know you have a limited budget, but have you seen the Adventure Offroad Campers?
We have their Grand Tourer Elite and yes it is pricey but very well designed and built.
http://www.adventurecampers.com.au/You might be able to pick one up second hand. It is a soft floor but is different to to others out there.
They are extremely quick and easy to setup and pack away. have a bigger than king size bed and bucket loads of storage, the left hand side is all kitchen at waist height.
We have a spare room that attaches to the main tent, but the son prefers an Oztent. Maybe that could be an option for the kids, they are easy to setup and pack away.