There are organizations like Get Stencils and All Things Thrifty who teach users how to make some stencils. They offer a variety of methods and the instructions are fairly simple to follow. There is no cost in learning how to make stencils.
Many craft stores carry a wide range of stencils such as Michael's and Jo-Anna. Great online sources for stencils are Spray Paint Stencils, Designer Stencils and Stencil Ease.
Making your own stencils is a breeze if you have access to an exacto knife. Tracing an outline on paper or doing a freehand sketch and then cutting around it with an exacto knife is a great way to make your own stencils.
Examples of skull stencils can be found from many different resources. Some websites with examples of skull stencils include iStencils and TCP Global.
You can try online at places like Zazzle you you can make your own. Just get some spray paint and make stencils and spray the logos on.
Usually for a booklet of stencils it costs around $10-$15.00 if you buy them from a online store. There are, however, sites that offer free, make-your-own stencils, like this one here: http://www.suite101.com/content/free-pumpkin-carving-stencils-a149319.
There are many places online where you can find printable butterfly stencils. These include Yahoo, Designer Stencils, Printable Stencils, All About Stencils, Stencil Ease and Examiner.
Orientaltrading.com has many Halloween pumpkin stencils to choose from! You can look at your local Walmart as well.
Patterned stencils really vary in price from how elaborate they are. You could try eBay if you are looking to get it cheap but try Michael's when they are on sale.
Home Depot, Cutting Edge Stencils, Shop Wright, Spray Paint Stencils, Hobby Lobby, Micheals, and Lowes all offer a great variety of wall stencils and other stencils.
Nail stencils are designs that they put on your nails.
You can purchase wall stencils online at many different sites. You can find them at Lowes, Home Depot and some lesser known stores.
Stencils can cost about $5 to $20 dollars depending on the quality. You can find some great stencils from http://www.coppergifts.com/cookie-cutters/pc/Jack-O-Lantern-Cookie-Stencil-Faces-p4111.htm