I think most people go the trailer route due to zoning laws.
I've looked in to this myself and found that most townships have a 500 square foot minimum for land owners looking to build a permanent housing structure on unimproved ground. Then you also have to consider other codes, like mandatory septic, well water, or even electric utility hookup. This could drive your costs way up.
I think going the trailer route is a perfectly acceptable way to go. Again check with the township zoning department to make sure you can get the appropriate permits to park a trailer, but it should prove to be a lot easier and less costly then going the conventional route.
You can actually buy plans to build your own tiny home on a trailer.
Check out both of these sites, I've heard nothing but good things.
Tiny Home Builders - Home
Tumbleweed Tiny House Company
Estimated cost to build yourself is around 20k, but if you search around people have built them for much less by using recycled materials and craigslist.