Go to tripadvisor, where you'll find detailed feedback on all travel agencies that offer tours to North Korea. ... I went there with Koryo Tours and have been very satisfied with them.
The least expensive way is to join a guided tour, and in our group, there were about 15 people, plus a Western guide, three North Korean guides, the North Korean camera man (we could buy the movie he made ... but I guess we weren't the only ones to get this video), and the bus driver.
You have to stay with the group at all times.
If you don't want to travel with a group, you can go "on your own", but you'll still have two North Korean guides and a driver with you. And the itinerary has to be planned in advance, even if it's just you.
Don't worry about the guides. Of course they have a different world view from your own, but otherwise, they are very nice and I feld comfortable around them.