See the Technical Standards PDF file web addy from the PDGA below. All distances are in centimeters so get out your conversion application for inches. In the PDF file the target specs start on page 4 and on page 5 are some schematic drawings and a measurement table. The PDGA does not specify the distance to the bottom of the basket off the playing surface. The PDF file does specify the height off the playing surface to the rim of the basket and the basket depth. So you will have to do some math to get a rough range of distance for bottom of the basket off the playing surface.
Note, since there is no maximum distance noted for basket depth in this PDF file (only minimum depth is specified), the basket could extend to the playing surface if a manufacturer wanted to put that much material into their basket design. Or, if you were building your own home-grown basket (and wanted to meet these guidelines for PDGA approved targets), you could use a trash can for the basket and have the bottom of the trash can resting on the playing surface as long as all of the guidelines are met in your design. That would make it tough to retrieve your disc though...essentially having to reach all the way to the ground to get your disc. :)