Stung Treng (also Stoeng Treng) is a small town in northeastern Cambodia, and can easily be described with the word "outpost" more than anything else. Many tourists heading to/from Laos pass through here, though few stay long as Ratanakiri and Kratie offer far more excitement, activities, and remedies.
Yes, Stung Treng does have what could be considered an airport, and Royal Phnom Penh Airways flies here for $50 one way, $95 round trip, for a journey taking about an hour. Though this is a fast way to get to Cambodia's remote northeastern provinces, it's a much better idea to head up here either overland or by boat, because there's so much to see in between here and Phnom Penh. Either option is also far cheaper than flying out here as well, so you should generally avoid the airport here unless you are pressed for time and want to get out to one of Cambodia's most remote regions.
Trucking from Kratie is an option, and will set you back 20-25,000 riel for riding in the back of the truck, and 25-30,000 riel if you wish to ride in the cabin. As discussed on the Kratie page, trucking is somewhat less safe than other modes of transport, and can take much longer. However, trucking in Cambodia puts you in much greater direct contact with the locals (as it's locals you'll be sharing a truck with most of the time), and isn't that one of the purposes of travelling?
Fast boats are probably the best way to get to Stung Treng based on the absolutely ridiculous state of the highways in this part of the country, but to and from Kratie they only run from July through to December. The cost of the trip is $8.
Since the town is so small, there's no point in using anything other than your own two feet to get you anywhere within the town itself. If you decide to see any of the area's limited sights, simply hire one of the few motodops around for no more than a couple of thousand riel.