I'm looking for a good inexpensive 3D design program. I don't need (or want) somthing at the level of the professional CAD software. I just want a reccomendation on which program (like the ones made for designing homes) you think is the best for doing simple projects. These projects would include designing houses/rooms and basic landscapes. I'm looking for somthing that is easy to use, but gives me enough options so that i'm not just drawing cubes all over the place. A key feature that i'm looking for is a good 3D walkthrough view (so i can look at what i designed in 3D, and move through the environment). I've heard that many of these programs take several seconds to render each frame making smooth travel through the environment impossible. I remember having an old Mac (50MHz) and it had a version of software like this and it worked great, however I now have a PC, and i'm looking for a Windows version.
Note: It would be a REALLY BIG BONUS if this software could be obtained for less than $50 (or about that amount).