I took the test this morning with a passing score of 98% (missed one question out of 60). Like most tests of this type, there were some ridiculously easy questions, some moderately difficult ones, and a couple of real head-scratchers.
My preparation consisted entirely of extensively studying the FAA Part 107 test guide and associated linked documents - in particular, the document outlining the regulation itself. and the Advisory Circular. I've never been a pilot, but I have a long and keen interest in aviation, so a lot of terminology, charts, etc. were at least somewhat familiar to me. My test prep cost only time, and no money. The test itself was $150.
Definitely know those sectionals, though - tons of questions on that. I would study some complex sectionals - I won't tell which airport they kept coming back to on the test that was complex, but you can use something like Orlando MCO as an example. Make sure you understand at any given point in, say, a 40-mile radius of MCO, what type of airspace you're in.
Also note that the chart legends are given to you, though unless you specifically check in the booklet, it may not be apparent and my proctor didn't mention this.
Glad to be through this - good luck to all of you going for the test. I found the prep to be somewhat fun, and definitely educational.