From what I remember sketch up make is free to download and last I checked I could get to the 3D warehouse from there, who knows though, maybe they changed it.
Also just a note about the free to download version. From what I understand it's a personal use product and therefore is not for commercial use, basically that you can't make money from your product if you use it. Of course I can't say I'm that well versed with these types of legal things, but just a fair warning to look into that kind of stuff and research if you want to make ad rev or whatnot.