The only free playhouse plan I've found is at www.buildeazy.com/wendyhouse.html. You'll have to convert the measurments but it's free.
The monster truck plan and a couple of playhouse plans that can be moved or taken down easily are listed at:
www.thewinfieldcollection.com (Monster truck)
Their plans are inexpensive and pretty cool.
A photo of the truck is not yet on the web site, but it is in the summer catalog. This site lists the materials needed to make the project, so you'll be able to get an idea of the cost of materials before you even purchase the plan.